Method for transmitting and receiving channel state information in wireless communication system and device for the same

ABSTRACT

A method for transmitting channel state information performed by a User Equipment (UE) may include receiving, from a base station, a bitmap for configuring codebook subset restriction (CSR) and reporting, to the base station, Channel State Information (CSI), when a number of antenna ports is configured as 16 or more and a number of layers associated with a rank indicator (RI) in the CSI is 3 or 4, a unit of multiple bits in a bitmap for configuring the CSR is associated with each precoder, and a reporting of precoding matrix indicator (PMI) corresponding to the precoder associated with the multiple bits is restricted in the CSI, when the CSR is indicated in any one of the multiple bits, and each bit in the bitmap for configuring the CSR is associated with each precoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/926,265, filed on Jul. 10, 2020, which is a continuation of U.S.patent application Ser. No. 16/319,225, filed on Jan. 18, 2019, which isa National Stage filing under 35 U.S.C. 371 of International ApplicationNo. PCT/KR2018/006713, filed on Jun. 14, 2018, which claims the benefitof U.S. Provisional Application No. 62/519,836, filed on Jun. 14, 2017,and No. 62/566,456, filed on Oct. 1, 2017, the contents of which are allhereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method for transmitting and receiving channel stateinformation in a wireless communication system that supports a multipleantenna system (particularly, 2 dimensional active antenna system (2DAAS)) and a device for supporting the same.

BACKGROUND

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

SUMMARY

An object of the present invention is to propose a method fortransmitting and receiving channel state information when a codebook isconfigured for codebook subset restriction and/or rank restriction, andthe like.

An object of the present invention is to propose a method forconfiguring/applying codebook subset restriction for the purpose ofinter-cell interference control when a codebook represented by types Iand II, and the like is used, which are used in New Radio AccessTechnology (NR).

Technological objects to be achieved by the present invention are notlimited to the aforementioned objects, and other objects that have notbeen described may be clearly understood by a person having ordinaryskill in the art to which the present invention pertains from thefollowing description.

According to an aspect of the present invention, a method fortransmitting channel state information in a wireless communicationsystem performed by a User Equipment (UE) may include receiving, from abase station, a bitmap for configuring codebook subset restriction (CSR)and reporting, to the base station, Channel State Information (CSI),when a number of antenna ports is configured as 16 or more and a numberof layers associated with a rank indicator (RI) in the CSI is 3 or 4, aunit of multiple bits in a bitmap for configuring the CSR is associatedwith each precoder, and a reporting of precoding matrix indicator (PMI)corresponding to the precoder associated with the multiple bits isrestricted in the CSI, when the CSR is indicated in any one of themultiple bits, and each bit in the bitmap for configuring the CSR isassociated with each precoder, and a reporting of PMI corresponding tothe precoder associated with a bit in which the CSR is indicated isrestricted in the CSI, except the case that the number of antenna portsis configured as 16 or more and the number of layers associated with theRI in the CSI is 3 or 4.

According to another aspect of the present invention, a method forreceiving channel state information in a wireless communication systemperformed by a base station may include transmitting, to a UserEquipment (UE), a bitmap for configuring codebook subset restriction(CSR) and receiving, from the UE, Channel State Information (CSI), whena number of antenna ports is configured as 16 or more and a number oflayers associated with a rank indicator (RI) in the CSI is 3 or 4,wherein a unit of multiple bits in a bitmap for configuring the CSR isassociated with each precoder, and a reporting of precoding matrixindicator (PMI) corresponding to the precoder associated with themultiple bits is restricted in the CSI, when the CSR is indicated in anyone of the multiple bits, and wherein each bit in the bitmap forconfiguring the CSR is associated with each precoder, and a reporting ofPMI corresponding to the precoder associated with a bit in which the CSRis indicated is restricted in the CSI, except the case that the numberof antenna ports is configured as 16 or more and the number of layersassociated with the RI in the CSI is 3 or 4.

Preferably, the bitmap for configuring the CSR may be commonly appliedwithout regard to the number of layers associated with the rankindicator (RI) in the CSI.

Preferably, when the number of antenna ports is configured as 16 or moreand the number of layers associated with the RI in the CSI is 3 or 4,the multiple bits includes three bits, and indexes of the three bitshave a relation of multiple with a specific number.

Preferably, the bit in the bitmap for configuring the CSR may belong toa unit of one or multiple bits.

Preferably, when the CSR is indicated in any one bit in the bitmap forconfiguring the CSR, depending on the number of a unit of multiple bitsto which the one bit belongs, a reporting of the PMI corresponding asingle or multiple precoders may be restricted.

Preferably, from the base station, a bitmap for a rank restrictionconfiguration may be transmitted to the UE.

Preferably, a bitwidth for reporting the rank indicator (RI) in the CSImay be determined depending on a number of rank indicators in which areporting is allowed by the bitmap for the rank restrictionconfiguration.

Preferably, a reporting of the rank indicator (RI) corresponding to thelayer associated with a bit in which a rank restriction in the bitmapfor the rank restriction configuration is indicated may be restricted inthe CSI.

Preferably, the UE may be a UE in which a codebook type of a singlepanel to which a linear combination is not applied is configured.

According to an embodiment of the present invention, a codebookconfiguration is applied, and accordingly, inter-cell interference maybe decreased.

In addition, according to an embodiment of the present invention, afeedback bit size of Channel State Information (CSI) is determined basedon a codebook configuration, and accordingly, CSI feedback overhead maybe reduced.

Effects which may be obtained by the present invention are not limitedto the aforementioned effects, and other effects that have not beendescribed may be clearly understood by a person having ordinary skill inthe art to which the present invention pertains from the followingdescription.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included herein as a part of thedescription for help understanding the present invention, provideembodiments of the present invention, and describe the technicalfeatures of the present invention with the description below.

FIGS. 1A and 1B illustrate the structure of a radio frame in a wirelesscommunication system to which the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for a downlink slot ina wireless communication system to which the present invention may beapplied.

FIG. 3 illustrates a structure of downlink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 4 illustrates a structure of uplink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 5 shows the configuration of a known MIMO communication system.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

FIG. 7 is a diagram for describing a basic concept of a codebook-basedprecoding in a wireless communication system to which the presentinvention may be applied.

FIGS. 8A and 8B illustrate reference signal patterns mapped to downlinkresource block pairs in a wireless communication system to which thepresent invention may be applied.

FIGS. 9A through 9C are diagrams illustrating resources to whichreference signals are mapped in a wireless communication system to whichthe present invention may be applied.

FIG. 10 illustrates a 2D-AAS having 64 antenna elements in a wirelesscommunication system to which the present invention may be applied.

FIG. 11 illustrates a system in which an eNB or UE has a plurality oftransmission/reception antennas capable of forming a 3D beam based onthe AAS in a wireless communication system to which the presentinvention may be applied.

FIG. 12 illustrates a 2D antenna system having cross polarizations in awireless communication system to which the present invention may beapplied.

FIGS. 13A and 13B illustrate a transceiver unit model in a wirelesscommunication system to which the present invention may be applied.

FIG. 14 illustrates a self-contained subframe structure to which thepresent invention may be applied.

FIG. 15 is a diagram schematically illustrating a hybrid beamformingstructure in the aspect of a TXRU and a physical antenna.

FIG. 16 is a diagram schematically illustrating a synchronization signalin DL transmission process and a beam sweeping operation for systeminformation.

FIG. 17 illustrates a panel antenna array to which the present inventionmay be applied.

FIG. 18 illustrates an antenna pattern gain when the codebook subsetrestriction is applied according to an embodiment of the presentinvention.

FIG. 19 is a diagram illustrating a method for transmitting andreceiving channel state information according to an embodiment of thepresent invention.

FIG. 20 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome embodiments of the present invention and are not intended todescribe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), gNB, aBase Transceiver System (BTS), an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to which the Present Invention May be Applied

FIGS. 1A and 1B show the structure of a radio frame in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

The size of a radio frame in the time domain is represented as amultiple of a time unit of T_s=1/(15000*2048). A UL and DL transmissionincludes the radio frame having a duration of T_f=307200*T_s=10 ms.

FIG. 1A exemplifies a radio frame structure type 1. The type 1 radioframe may be applied to both of full duplex FDD and half duplex FDD.

A radio frame includes 10 subframes. A radio frame includes 20 slots ofT_slot=15360*T_s=0.5 ms length, and 0 to 19 indexes are given to each ofthe slots. One subframe includes consecutive two slots in the timedomain, and subframe i includes slot 2i and slot 2i+1. The time requiredfor transmitting a subframe is referred to as a transmission timeinterval (TTI). For example, the length of the subframe i may be 1 msand the length of a slot may be 0.5 ms.

A UL transmission and a DL transmission I the FDD are distinguished inthe frequency domain. Whereas there is no restriction in the full duplexFDD, a UE may not transmit and receive simultaneously in the half duplexFDD operation.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1B shows frame structure type 2.

A type 2 radio frame includes two half frame of 153600*T_s=5 ms lengtheach. Each half frame includes 5 subframes of 30720*T_s=1 ms length.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Downlink- to-Uplink Uplink- Switch- Downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0  5 ms D S U U U DS U U U 1  5 ms D S U U D D S U U D 2  5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6  5 ms D S U U U D S U U D

Referring to Table 1, in each subframe of the radio frame, ‘D’represents a subframe for a DL transmission, ‘U’ represents a subframefor UL transmission, and ‘S’ represents a special subframe includingthree types of fields including a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and a Uplink Pilot Time Slot (UpPTS).

A DwPTS is used for an initial cell search, synchronization or channelestimation in a UE. A UpPTS is used for channel estimation in an eNB andfor synchronizing a UL transmission synchronization of a UE. A GP isduration for removing interference occurred in a UL owing to multi-pathdelay of a DL signal between a UL and a DL.

Each subframe i includes slot 2i and slot 2i+1 of T_slot=15360*T_s=0.5ms.

The UL-DL configuration may be classified into 7 types, and the positionand/or the number of a DL subframe, a special subframe and a UL subframeare different for each configuration.

A point of time at which a change is performed from DL to UL or a pointof time at which a change is performed from UL to DL is called aswitching point. The Switch-point periodicity means a cycle in which aUL subframe and a DL subframe are changed is identically repeated. Both5 ms and 10 ms are supported in the periodicity of a switching point. Inthe case that the periodicity of a switching point has a cycle of a 5 msDL-UL switching point, the special subframe S is present in each halfframe. In the case that the periodicity of a switching point has a cycleof a 5 ms DL-UL switching point, the special subframe S is present inthe first half frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly DL transmission. An UpPTS and a subframe subsequent to a subframeare always used for UL transmission.

Such DL-UL configurations may be known to both an eNB and UE as systeminformation. An eNB may notify UE of a change of the UL-DL allocationstate of a radio frame by transmitting only the index of UL-DLconfiguration information to the UE whenever the UL-DL configurationinformation is changed. Furthermore, configuration information is kindof DL control information and may be transmitted through a PhysicalDownlink Control Channel (PDCCH) like other scheduling information.Configuration information may be transmitted to all UEs within a cellthrough a broadcast channel as broadcasting information.

Table 2 represents configuration (length of DwPTS/GP/UpPTS) of a specialsubframe.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Normal Extended Normal Extended Special cycliccyclic cyclic cyclic subframe prefix in prefix in prefix in prefix inconfiguration DwPTS uplink uplink DwPTS uplink uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 4384 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of a radio subframe according to the example of FIGS. 1Aand 1B are just an example, and the number of subcarriers included in aradio frame, the number of slots included in a subframe and the numberof OFDM symbols included in a slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs N{circumflex over ( )}DL included in a downlink slot depends on adownlink transmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel. A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (a Radio Network Temporary Identifier(RNTI)) is masked to the CRC depending on the owner or use of a PDCCH.If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for a paging message, a paging indication identifier, forexample, a Paging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for system information, more specifically, a SystemInformation Block (SIB), a system information identifier, for example, aSystem Information-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 5 shows the configuration of a known MIMO communication system.

Referring to FIG. 5, if the number of transmission (Tx) antennas isincreased to N_T and the number of reception (Rx) antennas is increasedto N_R at the same time, a theoretical channel transmission capacity isincreased in proportion to the number of antennas, unlike in the casewhere a plurality of antennas is used only in a transmitter or areceiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_i by a maximum transfer rate R_o if one antenna isused.

R _(i)=min(N _(T) ,N _(R)  Equation 1

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below.

First, the spatial diversity method includes a space-time blockcode-series method and a space-time Trelis code-series method using adiversity gain and a coding gain at the same time. In general, theTrelis code-series method is better in terms of bit error rateimprovement performance and the degree of a code generation freedom,whereas the space-time block code-series method has low operationalcomplexity. Such a spatial diversity gain may correspond to an amountcorresponding to the product (N_T×N_R) of the number of transmissionantennas (N_T) and the number of reception antennas (N_R).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 5, it is assumed that N_T transmission antennasand NR reception antennas are present.

First, a transmission signal is described below. If the N_T transmissionantennas are present as described above, a maximum number of pieces ofinformation which can be transmitted are N_T, which may be representedusing the following vector.

s=[s ₁ ,s ₂ ,⋅ ⋅ ⋅ ,s _(N) _(T) ]^(T)  Equation 2

Meanwhile, transmission power may be different in each of pieces oftransmission information s_1, s_2, . . . , s_NT. In this case, if piecesof transmission power are P_1, P_2, . . . , P_NT, transmissioninformation having controlled transmission power may be representedusing the following vector.

ŝ=[ŝ ₁ ,ŝ ₂ , ⋅ ⋅ ⋅ ,ŝ _(N) _(T) ]^(T)=[P ₁ s ₁ ,P ₂ s ₂ , ⋅ ⋅ ⋅,P _(N)_(T) s _(N) _(T) ]^(T)  Equation 3

Furthermore, transmission information having controlled transmissionpower in the Equation 3 may be represented as follows using the diagonalmatrix P of transmission power.

$\begin{matrix}{\overset{\hat{}}{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Meanwhile, the information vector having controlled transmission powerin the Equation 4 is multiplied by a weight matrix W, thus forming N_Ttransmission signals x_1, x_2, . . . , x_NT that are actuallytransmitted. In this case, the weight matrix functions to properlydistribute the transmission information to antennas according to atransport channel condition. The following may be represented using thetransmission signals x_1, x_2, . . . , x_NT.

$\begin{matrix}{x = {\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{matrix} \rbrack = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & {\ldots} & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\overset{\hat{}}{s}}_{1} \\{\overset{\hat{}}{s}}_{2} \\\vdots \\{\overset{\hat{}}{s}}_{j} \\\vdots \\{\overset{\hat{}}{s}}_{N_{T}}\end{bmatrix}} = {{W\overset{\hat{}}{s}} = {WPs}}}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

In this case, w_ij denotes weight between an i-th transmission antennaand a j-th transmission information, and W is an expression of a matrixof the weight. Such a matrix W is called a weight matrix or precodingmatrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_R reception antennas are present, the reception signals y_1, y_2, .. . , y_NR of the respective antennas are represented as follows using avector y.

y=[y ₁ ,y ₂ ,⋅⋅⋅,y _(N) _(R) ]^(T)  Equation 6

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_ij. In this case, it is to be noted that in order of the index ofh_ij, the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 6, a channel from a total of N_T transmission antennasto a reception antenna i may be represented as follows.

h _(i) ^(T)=[h _(i1) ,h _(i2) ,⋅⋅⋅,h _(iN) _(T) ]  Equation 7

Furthermore, if all channels from the N_T transmission antenna to N_Rreception antennas are represented through a matrix expression, such asEquation 7, they may be represented as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix}\  = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n_1, n_2, . . . , n_NR added to the N_R receptionantennas, respectively, are represented using a vector as follows.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  Equation 9

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{matrix} \rbrack} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_R, and the number of columns becomes equal to the number oftransmission antennas N_T. That is, the channel matrix H becomes anN_R×N_T matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns. Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.

rank(H)≤min(N _(T) ,N _(R))  Equation 11

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a ‘rank’ for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The‘number of layers’ indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Hereinafter, in relation to the MIMO transmission techniques describedabove, a codebook-based precoding technique will be described in detail.

FIG. 7 is a diagram for describing a basic concept of a codebook-basedprecoding in a wireless communication system to which the presentinvention may be applied.

According to the codebook-based precoding technique, a transmitting-endand a receiving-end share codebook information that includes apredetermined number of precoding matrixes according to a transmissionrank, the number of antennas, and so on.

That is, in the case that feedback information is finite, theprecoding-based codebook technique may be used.

A receiving-end may measure a channel state through a receiving signal,and may feedback a finite number of preferred matrix information (i.e.,index of the corresponding precoding matrix) based on the codebookinformation described above. For example, a receiving-end may measure asignal in Maximum Likelihood (ML) or Minimum Mean Square Error (MMSE)technique, and may select an optimal precoding matrix.

FIG. 7 shows a case that a receiving-end transmits the precoding matrixinformation for each codeword to a transmitting-end, but the presentinvention is not limited thereto.

The transmitting-end that receives the feedback information from thereceiving-end may select a specific precoding matrix from the codebookbased on the received information. The transmitting-end that selects theprecoding matrix may perform precoding in a manner of multiplying layersignals, of which number amounts to a transmission rank, by the selectedprecoding matrix and may transmit the precoded transmission signal via aplurality of antennas. The number of rows in a precoding matrix is equalto the number of antennas, while the number of columns is equal to arank value. Since the rank value is equal to the number of layers, thenumber of the columns is equal to the number of the layers. Forinstance, when the number of transmitting antennas and the number oflayers are 4 and 2, respectively, a precoding matrix may include 4×2matrix. Equation 12 below represents an operation of mapping informationmapped to each layer to a respective antenna through the precodingmatrix in the case.

$\begin{matrix}{\begin{bmatrix}y_{1} \\y_{2} \\y_{3} \\y_{4}\end{bmatrix} = {\begin{bmatrix}p_{11} & y_{1} \\p_{12} & y_{1} \\p_{13} & y_{1} \\p_{14} & y_{1}\end{bmatrix} \cdot \begin{bmatrix}x_{1} \\x_{2}\end{bmatrix}}} & {{Equation}\mspace{14mu} 12}\end{matrix}$

Referring to Equation 12, information mapped to a layer includes x_1 andx_2 and each element p_ij of 4×2 matrix is a weight used for precoding.y_1, y_2, y_3 and y_4 indicate information mapped to antennas and may betransmitted via corresponding antennas by OFDM transmission schemes,respectively.

The receiving-end that receives the signal precoded and transmitted inthe transmitting-end may reconstruct the received signal by performinginverse processing of the precoding performed in the transmitting-end.Generally, since a precoding matrix satisfies such a unitary matrix (U)condition as U·U{circumflex over ( )}H=I (herein, U{circumflex over( )}H means an Hermit matrix of matrix U), the above-mentioned inverseprocessing of the precoding may be performed in a manner of multiplyingthe received signal by Hermit matrix P{circumflex over ( )}H of theprecoding matrix P used for the precoding performed by thetransmitting-end.

In addition, since the precoding is requested to have good performancefor antenna configurations of various types, it may be necessary toconsider performance for various antenna configurations in codebookdesign. In the following description, an exemplary configuration ofmultiple antennas is explained.

In the conventional 3GPP LTE system (e.g., system according to 3GPP LTERelease-8 or Release-9 Standard), since maximum four transmissionantennas are supported in DL, a codebook for four transmission antennasis designed. In the 3GPP LTE-A system evolved from the conventional 3GPPLTE system, maximum eight transmission antennas may be supported in DL.Accordingly, it may be necessary to design a precoding codebook thatprovides good performance for a DL transmission via maximum eighttransmission antennas.

Moreover, when a codebook is designed, generally required are constantmodulus property, finite alphabet, restriction on a codebook size,nested property, and providing good performance for various antennaconfigurations.

The constant modulus property means a property that amplitude of eachchannel component of a precoding matrix configuring a codebook isconstant. According to this property, no matter what kind of a precodingmatrix is used, power levels transmitted from all antennas may bemaintained equal to each other. Hence, it may be able to raiseefficiency in using a power amplifier.

The finite alphabet means to configure precoding matrixes usingquadrature phase shift keying (QPSK) alphabet (i.e., ±1, ±j) only excepta scaling factor in the case of two transmitting antennas, for example.Accordingly, when multiplication is performed on a precoding matrix by aprecoder, it may alleviate the complexity of calculation.

The codebook size may be restricted as a predetermined size or smaller.Since a size of a codebook increases, precoding matrixes for variouscases may be included in the codebook, and accordingly, a channel statusmay be more accurately reflected. However, the number of bits of aprecoding matrix indicator (PMI) correspondingly increases to causesignaling overhead.

The nested property means that a portion of a high rank precoding matrixis configured with a low rank precoding matrix. Thus, when thecorresponding precoding matrix is configured, an appropriate performancemay be guaranteed even in the case that a BS determines to perform a DLtransmission of a transmission rank lower than a channel rank indicatedby a rank indicator (RI) reported from a UE. In addition, according tothis property, complexity of channel quality information (CQI)calculation may be reduced. This is because calculation for a precodingmatrix selection may be shared in part when an operation of selecting aprecoding matrix from precoding matrixes designed for different ranks isperformed.

Providing good performance for various antenna configurations may meanthat providing performance over a predetermined level is required forvarious cases including a low correlated antenna configuration, a highcorrelated antenna configuration, a cross-polarized antennaconfiguration and the like.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission method and a signal known to both the transmissionside and the reception side when they are transmitted through a channelis chiefly used. The aforementioned signal is called a pilot signal orreference signal (RS).

Furthermore recently, when most of mobile communication systems transmita packet, they use a method capable of improving transmission/receptiondata efficiency by adopting multiple transmission antennas and multiplereception antennas instead of using one transmission antenna and onereception antenna used so far. When data is transmitted and receivedusing multiple input/output antennas, a channel state between thetransmission antenna and the reception antenna must be detected in orderto accurately receive the signal. Accordingly, each transmission antennamust have an individual reference signal.

In a mobile communication system, an RS may be basically divided intotwo types depending on its object. There are an RS having an object ofobtaining channel state information and an RS used for datademodulation. The former has an object of obtaining, by a UE, to obtainchannel state information in the downlink. Accordingly, a correspondingRS must be transmitted in a wideband, and a UE must be capable ofreceiving and measuring the RS although the UE does not receive downlinkdata in a specific subframe. Furthermore, the former is also used forradio resources management (RRM) measurement, such as handover. Thelatter is an RS transmitted along with corresponding resources when aneNB transmits the downlink. A UE may perform channel estimation byreceiving a corresponding RS and thus may demodulate data. Thecorresponding RS must be transmitted in a region in which data istransmitted.

A downlink RS includes one common RS (CRS) for the acquisition ofinformation about a channel state shared by all of UEs within a cell andmeasurement, such as handover, and a dedicated RS (DRS) used for datademodulation for only a specific UE. Information for demodulation andchannel measurement can be provided using such RSs. That is, the DRS isused for only data demodulation, and the CRS is used for the two objectsof channel information acquisition and data demodulation.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds an indicator related to channel quality, such as a channelquality indicator (CQI), a precoding matrix index (PMI) and/or a rankindicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of channel state information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. A UE may receive information about whether aDRS is present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIGS. 8A and 8B illustrate reference signal patterns mapped to downlinkresource block pairs in a wireless communication system to which thepresent invention may be applied.

Referring to FIGS. 8A and 8B, a downlink resource block pair, that is, aunit in which a reference signal is mapped may be represented in theform of one subframe in a time domain X 12 subcarriers in a frequencydomain. That is, in a time axis (an x axis), one resource block pair hasa length of 14 OFDM symbols in the case of a normal cyclic prefix (CP)(FIG. 7a ) and has a length of 12 OFDM symbols in the case of anextended cyclic prefix (CP) (FIG. 7b ). In the resource block lattice,resource elements (REs) indicated by ‘0’, ‘1’, ‘2’, and ‘3’ mean thelocations of the CRSs of antenna port indices ‘0’, ‘1’, ‘2’, and ‘3’,respectively, and REs indicated by ‘D’ mean the location of a DRS.

A CRS is described in more detail below. The CRS is a reference signalwhich is used to estimate the channel of a physical antenna and may bereceived by all UEs located within a cell in common. The CRS isdistributed to a full frequency bandwidth. That is, the CRS iscell-specific signal and is transmitted every subframe in a wideband.Furthermore, the CRS may be used for channel quality information (CSI)and data demodulation.

A CRS is defined in various formats depending on an antenna array on thetransmitting side (eNB). In the 3GPP LTE system (e.g., Release-8), an RSfor a maximum four antenna ports is transmitted depending on the numberof transmission antennas of an eNB. The side from which a downlinksignal is transmitted has three types of antenna arrays, such as asingle transmission antenna, two transmission antennas and fourtransmission antennas. For example, if the number of transmissionantennas of an eNB is two, CRSs for a No. 0 antenna port and a No. 1antenna port are transmitted. If the number of transmission antennas ofan eNB is four, CRSs for No. 0˜No. 3 antenna ports are transmitted. Ifthe number of transmission antennas of an eNB is four, a CRS pattern inone RB are shown in FIGS. 8A and 8B.

In the case that an eNB uses a single transmission antenna, referencesignals for a single antenna port are arrayed.

In the case that an eNB uses two transmission antennas, referencesignals for two transmission antenna ports are arrayed using a timedivision multiplexing (TDM) scheme and/or a frequency divisionmultiplexing (FDM) scheme. That is, different time resources and/ordifferent frequency resources are allocated in order to distinguishbetween reference signals for two antenna ports.

Furthermore, in the case that an eNB uses four transmission antennas,reference signals for four transmission antenna ports are arrayed usingthe TDM and/or FDM schemes. Channel information measured by thereception side (i.e., UE) of a downlink signal may be used to demodulatedata transmitted using a transmission scheme, such as singletransmission antenna transmission, transmission diversity, closed-loopspatial multiplexing, open-loop spatial multiplexing or amulti-user-multi-input/output (MIMO) antenna.

In the case that a multi-input multi-output antenna is supported, when aRS is transmitted by a specific antenna port, the RS is transmitted inthe locations of resource elements specified depending on a pattern ofthe RS and is not transmitted in the locations of resource elementsspecified for other antenna ports. That is, RSs between differentantennas do not overlap.

A DRS is described in more detail below. The DRS is used to demodulatedata. In multi-input multi-output antenna transmission, precoding weightused for a specific UE is combined with a transmission channeltransmitted by each transmission antenna when the UE receives an RS, andis used to estimate a corresponding channel without any change.

A 3GPP LTE system (e.g., Release-8) supports a maximum of fourtransmission antennas, and a DRS for rank 1 beamforming is defined. TheDRS for rank 1 beamforming also indicates an RS for an antenna portindex 5.

In an LTE-A system, that is, an advanced and developed form of the LTEsystem, the design is necessary to support a maximum of eighttransmission antennas in the downlink of an eNB. Accordingly, RSs forthe maximum of eight transmission antennas must be also supported. Inthe LTE system, only downlink RSs for a maximum of four antenna portshas been defined. Accordingly, in the case that an eNB has four to amaximum of eight downlink transmission antennas in the LTE-A system, RSsfor these antenna ports must be additionally defined and designed.Regarding the RSs for the maximum of eight transmission antenna ports,the aforementioned RS for channel measurement and the aforementioned RSfor data demodulation must be designed.

One of important factors that must be considered in designing an LTE-Asystem is backward compatibility, that is, that an LTE UE must welloperate even in the LTE-A system, which must be supported by the system.From an RS transmission viewpoint, in the time-frequency domain in whicha CRS defined in LTE is transmitted in a full band every subframe, RSsfor a maximum of eight transmission antenna ports must be additionallydefined. In the LTE-A system, if an RS pattern for a maximum of eighttransmission antennas is added in a full band every subframe using thesame method as the CRS of the existing LTE, RS overhead is excessivelyincreased.

Accordingly, the RS newly designed in the LTE-A system is basicallydivided into two types, which include an RS having a channel measurementobject for the selection of MCS or a PMI (channel state information-RSor channel state indication-RS (CSI-RS)) and an RS for the demodulationof data transmitted through eight transmission antennas (datademodulation-RS (DM-RS)).

The CSI-RS for the purpose of the channel measurement is characterizedin that it is designed for an object focused on channel measurementunlike the existing CRS used for objects for measurement, such aschannel measurement and handover, and for data demodulation.Furthermore, the CSI-RS may also be used for an object for measurement,such as handover. The CSI-RS does not need to be transmitted everysubframe unlike the CRS because it is transmitted for an object ofobtaining information about a channel state. In order to reduce overheadof a CSI-RS, the CSI-RS is intermittently transmitted on the time axis.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in a region in which the correspondingUE has been scheduled, that is, in the time-frequency domain in whichdata is received.

In the LTE-A system, a maximum of eight transmission antennas aresupported in the downlink of an eNB. In the LTE-A system, in the casethat RSs for a maximum of eight transmission antennas are transmitted ina full band every subframe using the same method as the CRS in theexisting LTE, RS overhead is excessively increased. Accordingly, in theLTE-A system, an RS has been separated into the CSI-RS of the CSImeasurement object for the selection of MCS or a PMI and the DM-RS fordata demodulation, and thus the two RSs have been added. The CSI-RS mayalso be used for an object, such as RRM measurement, but has beendesigned for a main object for the acquisition of CSI. The CSI-RS doesnot need to be transmitted every subframe because it is not used fordata demodulation. Accordingly, in order to reduce overhead of theCSI-RS, the CSI-RS is intermittently transmitted on the time axis. Thatis, the CSI-RS has a period corresponding to a multiple of the integerof one subframe and may be periodically transmitted or transmitted in aspecific transmission pattern. In this case, the period or pattern inwhich the CSI-RS is transmitted may be set by an eNB.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in the region in which scheduling isperformed for the corresponding UE, that is, only in the time-frequencydomain in which data is received.

In order to measure a CSI-RS, a UE must be aware of information aboutthe transmission subframe index of the CSI-RS for each CSI-RS antennaport of a cell to which the UE belongs, the location of a CSI-RSresource element (RE) time-frequency within a transmission subframe, anda CSI-RS sequence.

In the LTE-A system, an eNB has to transmit a CSI-RS for each of amaximum of eight antenna ports. Resources used for the CSI-RStransmission of different antenna ports must be orthogonal. When one eNBtransmits CSI-RSs for different antenna ports, it may orthogonallyallocate the resources according to the FDM/TDM scheme by mapping theCSI-RSs for the respective antenna ports to different REs.Alternatively, the CSI-RSs for different antenna ports may betransmitted according to the CDM scheme for mapping the CSI-RSs topieces of code orthogonal to each other.

When an eNB notifies a UE belonging to the eNB of information on aCSI-RS, first, the eNB must notify the UE of information about atime-frequency in which a CSI-RS for each antenna port is mapped.Specifically, the information includes subframe numbers in which theCSI-RS is transmitted or a period in which the CSI-RS is transmitted, asubframe offset in which the CSI-RS is transmitted, an OFDM symbolnumber in which the CSI-RS RE of a specific antenna is transmitted,frequency spacing, and the offset or shift value of an RE in thefrequency axis.

A CSI-RS is transmitted through one, two, four or eight antenna ports.Antenna ports used in this case are p=15, p=15, 16, p=15, . . . , 18,and p=15, . . . , 22, respectively. A CSI-RS may be defined for only asubcarrier interval Δf=15 kHz.

In a subframe configured for CSI-RS transmission, a CSI-RS sequence ismapped to a complex-valued modulation symbol a_k,l{circumflex over( )}(p) used as a reference symbol on each antenna port p as in Equation13.

$\begin{matrix}{{a_{k,l}^{(p)} = {w_{l^{''}} \cdot {r_{l,n_{s}}( m^{\prime} )}}}{k = {k^{\prime} + {12m} + \{ {{\begin{matrix}{- 0} & {{{{for}\mspace{14mu} p} \in \{ {15,16} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \{ {17,18} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 1} & {{{{for}\mspace{14mu} p} \in \{ {19,{20}} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 7} & {{{{for}\mspace{14mu} p} \in \{ {21,22} \}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 0} & {{{{for}\mspace{14mu} p} \in \{ {15,16} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 3} & {{{{for}\mspace{14mu} p} \in \{ {17,18} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \{ {19,{20}} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \{ {21,22} \}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\end{matrix}l} = {l^{\prime} + \{ {{\begin{matrix}l^{''} & {{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0} - 19},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{2l^{''}} & {{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 20} - 31},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\l^{''} & {{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0} - 27},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\end{matrix}w_{l^{''}}} = \{ {{{\begin{matrix}1 & {p \in \{ {15,17,19,21} \}} \\( {- 1} )^{l^{''}} & {p \in \{ {16,18,{20},{22}} \}}\end{matrix}l^{''}} = 0},{{1m} = 0},1,\ldots\mspace{14mu},{{N_{RB}^{DL} - {1m^{\prime}}} = {m + \lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \rfloor}}} } }} }}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

In Equation 13, (k′,l′) (wherein k′ is a subcarrier index within aresource block and l′ indicates an OFDM symbol index within a slot.) andthe condition of n_s is determined depending on a CSI-RS configuration,such as Table 3 or Table 4.

Table 3 illustrates the mapping of (k′,l′) from a CSI-RS configurationin a normal CP.

TABLE 3 CSI Number of CSI reference signals configured reference 1 or 24 8 signal n_(s) n_(s) n_(s) configuration (k′, l′) mod 2 (k′, l′) mod 2(k′, l′) mod 2 Frame 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 structure 1 (11, 2) 1(11, 2) 1 (11, 2) 1 type 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 1 and 2 3 (7, 2) 1(7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6(10, 2) 1 (10, 2) 1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1(8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame 20(11, 1) 1 (11, 1) 1 (11, 1) 1 structure 21 (9, 1) 1 (9, 1) 1 (9, 1) 1type 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 2 only 23 (10, 1) 1 (10, 1) 1 24(8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1)1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Table 4 illustrates the mapping of (k′,l′) from a CSI-RS configurationin an extended CP.

TABLE 4 CSI Number of CSI reference signals configured reference 1 or 24 8 signal n_(s) n_(s) n_(s) configuration (k′, l′) mod 2 (k′, l′) mod 2(k′, l′) mod 2 Frame 0 (11, 4) 0 (11, 4) 0 (11, 4) 0 structure 1 (9, 4)0 (9, 4) 0 (9, 4) 0 type 2 (10, 4) 1 (10, 4) 1 (10, 4) 1 1 and 2 3 (9,4) 1 (9, 4) 1 (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6 (4, 4)1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 0 11 (0,4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Frame 16 (11, 1) 1(11, 1) 1 (11, 1) 1 structure 17 (10, 1) 1 (10, 1) 1 (10, 1) 1 type 18(9, 1) 1 (9, 1) 1 (9, 1) 1 2 only 19 (5, 1) 1 (5, 1) 1 20 (4, 1) 1(4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24 (6, 1) 1 25(2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, in the transmission of a CSI-RS, inorder to reduce inter-cell interference (ICI) in a multi-cellenvironment including a heterogeneous network (HetNet) environment, amaximum of 32 different configurations (in the case of a normal CP) or amaximum of 28 different configurations (in the case of an extended CP)are defined.

The CSI-RS configuration is different depending on the number of antennaports and a CP within a cell, and a neighboring cell may have a maximumof different configurations. Furthermore, the CSI-RS configuration maybe divided into a case where it is applied to both an FDD frame and aTDD frame and a case where it is applied to only a TDD frame dependingon a frame structure.

(k′,l′) and n_s are determined depending on a CSI-RS configuration basedon Table 3 and Table 4, and time-frequency resources used for CSI-RStransmission are determined depending on each CSI-RS antenna port.

FIGS. 9A through 9C is a diagram illustrating resources to whichreference signals are mapped in a wireless communication system to whichthe present invention may be applied.

FIG. 9A shows twenty types of CSI-RS configurations available for CSI-RStransmission by one or two CSI-RS antenna ports, FIG. 9B shows ten typesof CSI-RS configurations available for four CSI-RS antenna ports, andFIG. 9C shows five types of CSI-RS configurations available for eightCSI-RS antenna ports.

As described above, radio resources (i.e., an RE pair) in which a CSI-RSis transmitted are determined depending on each CSI-RS configuration.

In the case that one or two antenna ports are configured for CSI-RStransmission with respect to a specific cell, the CSI-RS is transmittedon radio resources on a configured CSI-RS configuration of the twentytypes of CSI-RS configurations shown in FIG. 9A.

Likewise, when four antenna ports are configured for CSI-RS transmissionwith respect to a specific cell, a CSI-RS is transmitted on radioresources on a configured CSI-RS configuration of the ten types ofCSI-RS configurations shown in FIG. 9B. Furthermore, when eight antennaports are configured for CSI-RS transmission with respect to a specificcell, a CSI-RS is transmitted on radio resources on a configured CSI-RSconfiguration of the five types of CSI-RS configurations shown in FIG.9C.

A CSI-RS for each antenna port is subjected to CDM for every two antennaports (i.e., {15,16}, {17,18}, {19,20} and {21,22}) on the same radioresources and transmitted. For example, in the case of antenna ports 15and 16, CSI-RS complex symbols for the respective antenna ports 15 and16 are the same, but are multiplied by different types of orthogonalcode (e.g., Walsh code) and mapped to the same radio resources. Thecomplex symbol of the CSI-RS for the antenna port 15 is multiplied by[1, 1], and the complex symbol of the CSI-RS for the antenna port 16 ismultiplied by [1 −1] and mapped to the same radio resources. The same istrue of the antenna ports {17,18}, {19,20} and {21,22}.

A UE may detect a CSI-RS for a specific antenna port by multiplying codeby which a transmitted symbol has been multiplied. That is, atransmitted symbol is multiplied by the code [11] multiplied in order todetect the CSI-RS for the antenna port 15, and a transmitted symbol ismultiplied by the code [1 −1] multiplied in order to detect the CSI-RSfor the antenna port 16.

Referring to FIGS. 9A to 9C, in the case of the same CSI-RSconfiguration index, radio resources according to a CSI-RS configurationhaving a large number of antenna ports include radio resources having asmall number of CSI-RS antenna ports. For example, in the case of aCSI-RS configuration 0, radio resources for the number of eight antennaports include both radio resources for the number of four antenna portsand radio resources for the number of one or two antenna ports.

A plurality of CSI-RS configurations may be used in one cell. 0 or oneCSI-RS configuration may be used for a non-zero power (NZP) CSI-RS, and0 or several CSI-RS configurations may be used for a zero power (ZP)CSI-RS.

For each bit set to 1 in a zeropower (ZP) CSI-RS (‘ZeroPowerCSI-RS) thatis a bitmap of 16 bits configured by a high layer, a UE assumes zerotransmission power in REs (except a case where an RE overlaps an REassuming a NZP CSI-RS configured by a high layer) corresponding to thefour CSI-RS columns of Table 3 and Table 4. The most significant bit(MSB) corresponds to the lowest CSI-RS configuration index, and nextbits in the bitmap sequentially correspond to next CSI-RS configurationindices.

A CSI-RS is transmitted only in a downlink slot that satisfies thecondition of (n_s mod 2) in Table 3 and Table 4 and a subframe thatsatisfies the CSI-RS subframe configurations.

In the case of the frame structure type 2 (TDD), a CSI-RS is nottransmitted in a special subframe, a synchronization signal (SS), asubframe colliding against a PBCH or SystemInformationBlockType1 (SIB 1)Message transmission or a subframe configured to paging messagetransmission.

Furthermore, an RE in which a CSI-RS for any antenna port belonging toan antenna port set S (S={15}, S={15,16}, S={17,18}, S={19,20} orS={21,22}) is transmitted is not used for the transmission of a PDSCH orfor the CSI-RS transmission of another antenna port.

Time-frequency resources used for CSI-RS transmission cannot be used fordata transmission. Accordingly, data throughput is reduced as CSI-RSoverhead is increased. By considering this, a CSI-RS is not configuredto be transmitted every subframe, but is configured to be transmitted ineach transmission period corresponding to a plurality of subframes. Inthis case, CSI-RS transmission overhead can be significantly reducedcompared to a case where a CSI-RS is transmitted every subframe.

A subframe period (hereinafter referred to as a “CSI transmissionperiod”) T_CSI-RS and a subframe offset Δ_CSI-RS for CSI-RS transmissionare shown in Table 5.

Table 5 illustrates CSI-RS subframe configurations.

TABLE 5 CSI-RS CSI-RS CSI-RS- periodicity subframe SubframeConfigT_(CSI-RS) offset Δ_(CSI-RS) I-_(CSI-RS) (subframes) (subframes) 0-4  5I_(CSI-RS)  5-14 10 I_(CSI-RS) −5  15-34 20 I_(CSI-RS) −15 35-74 40I_(CSI-RS) −35  75-154 80 I_(CSI-RS) −75

Referring to Table 5, the CSI-RS transmission period T_CSI-RS and thesubframe offset Δ_CSI-RS are determined depending on the CSI-RS subframeconfiguration I_CSI-RS.

The CSI-RS subframe configuration of Table 5 may be configured as one ofthe aforementioned ‘SubframeConfig’ field and‘zeroTxPowerSubframeConfig’ field. The CSI-RS subframe configuration maybe separately configured with respect to an NZP CSI-RS and a ZP CSI-RS.

A subframe including a CSI-RS satisfies Equation 14.

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  Equation 14

In Equation 14, T_CSI-RS means a CSI-RS transmission period, Δ_CSI-RSmeans a subframe offset value, n_f means a system frame number, and n_smeans a slot number.

In the case of a UE in which the transmission mode 9 has been configuredwith respect to a serving cell, one CSI-RS resource configuration may beconfigured for the UE. In the case of a UE in which the transmissionmode 10 has been configured with respect to a serving cell, one or moreCSI-RS resource configuration (s) may be configured for the UE.

In the current LTE standard, a CSI-RS configuration includes an antennaport number (antennaPortsCount), a subframe configuration(subframeConfig), and a resource configuration (resourceConfig).Accordingly, the a CSI-RS configuration provides notification that aCSI-RS is transmitted how many antenna port, provides notification ofthe period and offset of a subframe in which a CSI-RS will betransmitted, and provides notification that a CSI-RS is transmitted inwhich RE location (i.e., a frequency and OFDM symbol index) in acorresponding subframe.

Specifically, the following parameters for each CSI-RS (resource)configuration are configured through high layer signaling.

-   -   In the case that transmission mode 10 is configured, a CSI-RS        resource configuration identifier    -   A CSI-RS port number (antennaPortsCount): a parameter (e.g., one        CSI-RS port, two CSI-RS ports, four CSI-RS ports or eight CSI-RS        ports) indicative of the number of antenna ports used for CSI-RS        transmission    -   A CSI-RS configuration (resourceConfig) (refer to Table 3 and        Table 4): a parameter regarding a CSI-RS allocation resource        location    -   A CSI-RS subframe configuration (subframeConfig, that is,        I_CSI-RS) (refer to Table 5): a parameter regarding the period        and/or offset of a subframe in which a CSI-RS will be        transmitted    -   In the case that transmission mode 9 is configured, transmission        power P_C for CSI feedback: in relation to the assumption of a        UE for reference PDSCH transmission power for feedback, when the        UE derives CSI feedback and takes a value within a [−8, 15] dB        range in a 1-dB step size, PS is assumed to be the ratio of        energy per resource element (EPRE) per PDSCH RE and a CSI-RS        EPRE.    -   In the case that transmission mode 10 is configured,        transmission power P_C for CSI feedback with respect to each CSI        process. When CSI subframe sets C_CSI,0 and C_CSI,1 are        configured by a high layer with respect to a CSI process, P_C is        configured for each CSI subframe set in the CSI process.    -   A pseudo-random sequence generator parameter n_ID    -   In the case that transmission mode 10 is configured, a high        layer parameter ‘qcl-CRS-Info-r11’ including a QCL scrambling        identifier for a quasico-located (QCL) type B UE assumption        (qcl-ScramblingIdentity-r11), a CRS port count        (crs-PortsCount-r11), and an MBSFN subframe configuration list        (mbsfn-SubframeConfigList-r11) parameter.

When a CSI feedback value derived by a UE has a value within the [−8,15] dB range, P_C is assumed to be the ration of PDSCH EPRE to CSI-RSEPRE. In this case, the PDSCH EPRE corresponds to a symbol in which theratio of PDSCH EPRE to CRS EPRE is ρ_A.

A CSI-RS and a PMCH are not configured in the same subframe of a servingcell at the same time.

In the frame structure type 2, in the case that four CRS antenna portsare configured, a CSI-RS configuration index belonging to the [20-31]set (refer to Table 3) in the case of a normal CP or a CSI-RSconfiguration index belonging to the [16-27] set (refer to Table 4) inthe case of an extended CP is not configured in a UE.

A UE may assume that the CSI-RS antenna port of a CSI-RS resourceconfiguration has a QCL relation with delay spread, Doppler spread,Doppler shift, an average gain and average delay.

A UE in which the transmission mode 10 and the QCL type B have beenconfigured may assume that antenna ports 0-3 corresponding to a CSI-RSresource configuration and antenna ports 15-22 corresponding to a CSI-RSresource configuration have QCL relation with Doppler spread and Dopplershift.

In the case of a UE in which the transmission modes 1-9 are configured,one ZP CSI-RS resource configuration may be configured in the UE withrespect to a serving cell. In the case of a UE in which the transmissionmode 10 has been configured, one or more ZP CSI-RS resourceconfigurations may be configured in the UE with respect to a servingcell.

The following parameters for a ZP CSI-RS resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration list (zeroTxPowerResourceConfigList)        (refer to Table 3 and Table 4): a parameter regarding a        zero-power CSI-RS configuration    -   The ZP CSI-RS subframe configuration (eroTxPowerSubframeConfig,        that is, I_CSI-RS) (refer to Table 5): a parameter regarding the        period and/or offset of a subframe in which a zero-power CSI-RS        is transmitted

A ZP CSI-RS and a PMCH are not configured in the same subframe of aserving cell at the same time.

In the case of a UE in which the transmission mode 10 has beenconfigured, one or more channel state information—interferencemeasurement (CSI-IM) resource configurations may be configured in the UEwith respect to a serving cell.

The following parameters for each CSI-IM resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration (refer to Table 3 and Table 4)    -   The ZP CSI RS subframe configuration I_CSI-RS (refer to Table 5)

A CSI-IM resource configuration is the same as any one of configured ZPCSI-RS resource configurations.

A CSI-IM resource and a PMCH are not configured within the same subframeof a serving cell at the same time.

Massive MIMO

A MIMO system having a plurality of antennas may be called a massiveMIMO system and attracts attention as a means for improving spectralefficiency, energy efficiency and processing complexity.

Recently, the massive MIMO system has been discussed in order to meetrequirements for spectral efficiency of future mobile communicationsystems in 3GPP. Massive MIMO is also called full-dimension MIMO(FD-MIMO).

LTE release-12 and following wireless communication systems considerintroduction of an active antenna system (AAS).

Distinguished from conventional passive antenna systems in which anamplifier capable of adjusting the phase and magnitude of a signal isseparated from an antenna, the AAS is configured in such a manner thateach antenna includes an active element such as an amplifier.

The AAS does not require additional cables, connectors and hardware forconnecting amplifiers and antennas and thus has high energy efficiencyand low operation costs. Particularly, the AAS supports electronic beamcontrol per antenna and thus can realize enhanced MIMO for formingaccurate beam patterns in consideration of a beam direction and a beamwidth or 3D beam patterns.

With the introduction of enhanced antenna systems such as the AAS,massive MIMO having a plurality of input/output antennas and amulti-dimensional antenna structure is also considered. For example,when a 2D antenna array instead of a conventional linear antenna arrayis formed, a 3D beam pattern can be formed using active antennas of theAAS.

FIG. 10 illustrates a 2D AAS having 64 antenna elements in a wirelesscommunication system to which the present invention is applicable.

FIG. 10 illustrates a normal 2D antenna array. A case in which Nt=Nv·Nhantennas are arranged in a square form, as shown in FIG. 10, may beconsidered. Here, Nh indicates the number of antenna columns in thehorizontal direction and Nv indicates the number of antenna rows in thevertical direction.

When the aforementioned 2D antenna array is used, radio waves can becontrolled in both the vertical direction (elevation) and the horizontaldirection (azimuth) to control transmitted beams in a 3D space. Awavelength control mechanism of this type may be referred to as 3Dbeamforming.

FIG. 11 illustrates a system in which an eNB or a UE has a plurality oftransmission/reception antennas capable of forming AAS based 3D beams ina wireless communication system to which the present invention isapplicable.

FIG. 11 schematizes the above-described example and illustrates a 3DMIMO system using a 2D antenna array (i.e., 2D-AAS).

From the viewpoint of transmission antennas, quasi-static or dynamicbeam formation in the vertical direction as well as the horizontaldirection of beams can be performed when a 3D beam pattern is used. Forexample, application such as sector formation in the vertical directionmay be considered.

From the viewpoint of reception antennas, a signal power increase effectaccording to an antenna array gain can be expected when a received beamis formed using a massive reception antenna. Accordingly, in the case ofuplink, an eNB can receive signals transmitted from a UE through aplurality of antennas, and the UE can set transmission power thereof toa very low level in consideration of the gain of the massive receptionantenna.

FIG. 12 illustrates a 2D antenna system having cross polarization in awireless communication system to which the present invention isapplicable.

2D planar antenna array model considering polarization may beschematized as shown in FIG. 12.

Distinguished from conventional MIMO systems using passive antennas,systems based on active antennas can dynamically control gains ofantenna elements by applying a weight to an active element (e.g.,amplifier) attached to (or included in) each antenna element. Since aradiation pattern depends on antenna arrangement such as the number ofantenna elements and antenna spacing, an antenna system can be modeledat an antenna element level.

The antenna arrangement model as shown in FIG. 12 may be represented by(M, N, P) which corresponds to parameters characterizing an antennaarrangement structure.

M indicates the number of antenna elements having the same polarizationin each column (i.e., in the vertical direction) (i.e., the number ofantenna elements having +45° slant in each column or the number ofantenna elements having −45° slant in each column).

N indicates the number of columns in the horizontal direction (i.e., thenumber of antenna elements in the horizontal direction).

P indicates the number of dimensions of polarization. P=2 in the case ofcross polarization as shown in FIG. 12, whereas P=1 in the case ofco-polarization.

An antenna port may be mapped to a physical antenna element. The antennaport may be defined by a reference signal associated therewith. Forexample, antenna port 0 may be associated with a cell-specific referencesignal (CRS) and antenna port 6 may be associated with a positioningreference signal (PRS) in the LTE system.

For example, antenna ports and physical antenna elements may beone-to-one mapped. This may correspond to a case in which a singlecross-polarization antenna element is used for downlink MIMO or downlinktransmit diversity. For example, antenna port 0 may be mapped to asingle physical antenna element, whereas antenna port 1 may be mapped toanother physical antenna element. In this case, two downlinktransmissions are present in terms of a UE. One is associated with areference signal for antenna port 0 and the other is associated with areference signal for antenna port 1.

Alternatively, a single antenna port may be mapped to multiple physicalantenna elements. This may correspond to a case in which a singleantenna port is used for beamforming. Beamforming can cause downlinktransmission to be directed to a specific UE by using multiple physicalantenna elements. This can be accomplished using an antenna arraycomposed of multiple columns of multiple cross-polarization antennaelements in general. In this case, a single downlink transmissionderived from a single antenna port is present in terms of a UE. One isassociated with a CRS for antenna port 0 and the other is associatedwith a CRS for antenna port 1.

That is, an antenna port represents downlink transmission in terms of aUE rather than substantial downlink transmission from a physical antennaelement in an eNB.

Alternatively, a plurality of antenna ports may be used for downlinktransmission and each antenna port may be multiple physical antennaports. This may correspond to a case in which antenna arrangement isused for downlink MIMO or downlink diversity. For example, antenna port0 may be mapped to multiple physical antenna ports and antenna port 1may be mapped to multiple physical antenna ports. In this case, twodownlink transmissions are present in terms of a UE. One is associatedwith a reference signal for antenna port 0 and the other is associatedwith a reference signal for antenna port 1.

In FD-MIMO, MIMO precoding of a data stream may be subjected to antennaport virtualization, transceiver unit (TXRU) virtualization and anantenna element pattern.

In antenna port virtualization, a stream on an antenna port is precodedon TXRU. In TXRU virtualization, a TXRU signal is precoded on an antennaelement. In the antenna element pattern, a signal radiated from anantenna element may have a directional gain pattern.

In conventional transceiver modeling, static one-to-on mapping betweenan antenna port and TXRU is assumed and TXRU virtualization effect isintegrated into a (TXRU) antenna pattern including both the effects ofthe TXRU virtualization and antenna element pattern.

Antenna port virtualization may be performed through afrequency-selective method. In LTE, an antenna port is defined alongwith a reference signal (or pilot). For example, for transmission ofdata precoded on an antenna port, a DMRS is transmitted in the samebandwidth as that for a data signal and both the DMRS and the datasignal are precoded through the same precoder (or the same TXRUvirtualization precoding). For CSI measurement, a CSI-RS is transmittedthrough multiple antenna ports. In CSI-RS transmission, a precoder whichcharacterizes mapping between a CSI-RS port and TXRU may be designed asan eigen matrix such that a UE can estimate a TXRU virtualizationprecoding matrix for a data precoding vector.

1D TXRU virtualization and 2D TXRU virtualization are discussed as TXRUvirtualization methods, which will be described below with reference tothe drawings.

FIGS. 13A and 13B illustrate transceiver unit models in a wirelesscommunication system to which the present invention is applicable.

In 1D TXRU virtualization, M_TXRU TXRUs are associated with M antennaelements in a single-column antenna arrangement having the samepolarization.

In 2D TXRU virtualization, a TXRU model corresponding to the antennaarrangement model (M, N, P) of FIG. 12 may be represented by (M_TXRU, N,P). Here, M_TXRU denotes the number of 2D TXRUs present in the samecolumn and the same polarization, and M_TXRU≤M all the time. That is, atotal number of TXRUs is M_TXRU×N×P.

TXRU virtualization models may be divided into TXRU virtualization modeloption-1: sub-array partition model as shown in FIG. 13A and TXRUvirtualization model option-2: full-connection model as shown in FIG.13B according to correlation between antenna elements and TXRU.

Referring to FIG. 13A, antenna elements are partitioned into multipleantenna element groups and each TXRU is connected to one of the groupsin the case of the sub-array partition model.

Referring to FIG. 13B, multiple TXRU signals are combined and deliveredto a single antenna element (or antenna element array) in the case ofthe full-connection model.

In FIGS. 13A and 13B, q is a transmission signal vector of Mco-polarized antenna elements in a single column, w is a wideband TXRUvirtualization weight vector, W is a wideband TXRU virtualization weightmatrix, and x is a signal vector of M_TXRU TXRUs.

Here, mapping between antenna ports and TXRUs may be 1-to-1 or 1-to-manymapping.

FIGS. 13A and 13B shows an example of TXRU-to-antenna element mappingand the present invention is not limited thereto. The present inventionmay be equally applied to mapping between TXRUs and antenna elementsrealized in various manners in terms of hardware.

OFDM Numerology

As more communication devices require greater communication capacity, anecessity of mobile broadband communication which is more improved thanthe existing radio access technology (RAT) has been raised. In addition,the massive MTC (Machine Type Communications) that provides variousservices anytime and anywhere by connecting a plurality of devices andobjects is also one of important issues, which is considered in a nextgeneration communication. Moreover, it has been discussed a design of acommunication system in which a service and/or a UE sensitive toreliability and latency. As such, an introduction of a next generationRAT has been discussed currently, which considers enhanced mobilebroadband communication, massive MTC, Ultra-Reliable and Low LatencyCommunication (URLLC), and the like, and such a technology is commonlyreferred to as “new RAT (NR)”.

Hereinafter, the Radio Access Network to which NR is applied in thepresent disclosure may be commonly called as New Generation-RAN (NG-RAN)or gNB, and this may be commonly called as a base station.

Self-Contained Subframe Structure

In TDD system, in order to minimize data transmission latency, aself-contained subframe structure to which a control channel and a datachannel are Time Division Multiplexed (TDMed) as shown in FIG. 14 hasbeen considered in 5 Generation new RAT.

FIG. 14 illustrates a self-contained subframe structure to which thepresent invention may be applied.

The shaded area in FIG. 14 shows a transport region of a physicalchannel (e.g., PDCCH) for forwarding DCI, and the dark area shows atransport region of a physical channel (e.g., PUCCH) for forwardingUplink Control Information (UCI).

The control information that an eNB forwards to a UE through DCIincludes information of a cell configuration that the UE needs to know,DL-specific information such as DL scheduling, and the like, and/orUL-specific information such as UL grant. Further, the controlinformation that an eNB forwards to a UE through UCI includes ACK/NACKreport of HARQ for a DL data, CSI report for DL channel state, and/orScheduling Request (SR), and so on.

The area not marked in FIG. 14 may be used for transport region of aphysical channel (e.g., PDSCH) for a downlink (DL) data and a transportregion of a physical channel (e.g., PUSCH) for an uplink (UL) data. Inthe characteristics of such a structure, a DL transmission and a ULtransmission may be sequentially progressed in a subframe (SF), a DLdata may be transmitted, and a UL ACK/NACK may be received in thecorresponding SF. Consequently, according to this structure, a timerequired for retransmitting data is reduced when a data transmissionerror occurs, and owing to this, the delay till the final dataforwarding may be minimized.

In such a self-contained subframe structure, a time gap is required fora process that an eNB and a UE switch from a transmission mode to areception mode or a process that an eNB and a UE switch from a receptionmode to a transmission mode. For this, a part of OFDM symbols on thetiming switching from DL to UL may be setup as GP, and such a subframetype may be referred to as ‘self-contained SF’.

Analog Beamforming

In Millimeter Wave (mmW) band, a wavelength becomes short and aninstallation of a plurality of antenna elements is available in the samearea. That is, the wavelength in 30 GHz band is 1 cm, and accordingly,an installation of total 64(8×8) antenna elements is available in2-dimensional arrangement shape with 0.5 lambda (wavelength) intervalsin 5 by 5 cm panel. Therefore, in mmW band, beamforming (BF) gain isincreased by using a plurality of antenna elements, and accordingly,coverage is increased or throughput becomes higher.

In this case, each antenna element has a Transceiver Unit (TXRU) suchthat it is available to adjust a transmission power and a phase, andindependent beamforming is available for each frequency resource.However, it has a problem that effectiveness is degraded in a costaspect when TXRUs are installed in all of about 100 antenna elements.Accordingly, a method has been considered to map a plurality of antennaelements in a single TXRU and to adjust a direction of beam by an analogphase shifter. Such an analog beamforming technique may make only onebeam direction throughout the entire band, and there is a disadvantagethat frequency selective beamforming is not available.

As a middle form between a Digital BF and an analog BF, B number ofhybrid BF may be considered which is smaller than Q number of antennaelement. In this case, directions of beams that may be transmittedsimultaneously are limited lower than B number; even it is changedaccording to a connection scheme between B number of TXRUs and Q numberof antenna elements.

In addition, in the case that multiple antennas are used in the New RATsystem, a hybrid beamforming technique has emerged, in which digitalbeamforming and analogue beamforming are combined. In this case, theanalog beamforming (or radio frequency (RF) beamforming) means anoperation of performing precoding (or combining) in an RF terminal. Inthe hybrid beamforming technique, each of a Baseband terminal and an RFterminal performs precoding (or combining), and owing to this, there isan advantage that a performance approaching to the digital beamformingcan be attained while the number of RF chains and the number of digital(D)/analog (A) (or A/D) converters are reduced. For the convenience ofdescription, a hybrid beamforming structure may be represented by Ntransceiver units (TXRUs) and M physical antennas. Then, the digitalbeamforming for L data layers that are going to be transmitted in atransmitter may be represented by N by L matrix. Then, the analogbeamforming is applied that the transformed N digital signals aretransformed to analog signals through a TXRU, and then represented by Mby N matrix.

FIG. 15 is a diagram schematically illustrating a hybrid beamformingstructure in the aspect of a TXRU and a physical antenna.

FIG. 15 exemplifies the case that the number of digital beams is L andthe number of analog beams is N.

In the New RAT system, a direction has been considered: it is designedthat an eNB may change the analog beamforming in a symbol unit, and moreefficient beamforming is supported to a UE located in a specific area.Furthermore, when specific N TXRUs and M RF antennas shown in FIG. 15are defined as a single antenna panel, in the New RAT system, the way ofintroducing a plurality of antenna panels has been also considered, towhich independent hybrid beamforming may be applied.

In the case that an eNB utilizes a plurality of analog beams, an analogbeam beneficial to receive a signal may be changed according to each UE.Accordingly, a beam sweeping operation has been considered that for atleast synchronization signal, system information, paging, and the like,a plurality of analog beams that an eNB is going to apply in a specificSubframe (SF) is changed for each symbol such that all UEs havereception changes.

FIG. 16 is a diagram schematically illustrating a synchronization signalin DL transmission process and a beam sweeping operation for systeminformation.

The physical resource (or physical channel) on which system informationof the New RAT system is transmitted in FIG. 16 is referred to as xphysical broadcast channel (xPBCH).

Referring to FIG. 16, the analog beams belonged to different antennapanels in a single symbol may be transmitted simultaneously. In order tomeasure a channel for each analog beam, as shown in FIG. 16, anintroduction of a beam RS (BRS) has been discussed that a beam RS (BRS)is introduced, which is an RS to which a single analog beam(corresponding to a specific antenna panel) is applied and transmitted.The BRS may be defined for a plurality of antenna ports, and eachantenna port of the BRS may correspond to a single analog beam. At thistime, different from the BRS, a synchronization signal or xPBCH may betransmitted and all analog beams in an analog beam group may be appliedso as to be received well by an arbitrary UE.

RRM Measurement in LTE

The LTE system supports an RRM operation for power control, scheduling,cell search, cell research, handover, radio link or connectionmonitoring, connection establishment/re-establishment, and so on. Aserving cell may request RRM measurement information, which is ameasurement value for performing an RRM operation to a UE.Representatively, in the LTE system, a UE may measure/obtain informationsuch as reference signal received power (RSRP), reference signalreceived quality (RSRQ), and the like and report it. Particularly, inthe LTE system, a UE receives ‘measConfig’ as a higher layer signal foran RRM measurement from a serving cell. The UE may measure RSRP or RSRQaccording to the information of ‘measConfig’. Herein, the definition ofRSRP, RSRQ and RSSI according to TS 36.214 document of the LTE system isas follows.

1) RSRP

RSRP is defined as the linear average over the power contributions (in[W]) of the resource elements that carry cell-specific RS (CRS) withinthe considered measurement frequency bandwidth. For RSRP determination,the CRS R0 according TS 36.211 [3] shall be used. In the case that a UEmay reliably detect that R1 is available, it may use R1 in addition toR0 to determine RSRP.

The reference point for the RSRP shall be the antenna connector of theUE.

In the case that receiver diversity is in use by the UE, the reportedvalue shall not be lower than the corresponding RSRP of any of theindividual diversity branches.

2) RSRQ

Reference Signal Received Quality (RSRQ) is defined as the ratioN×RSRP/(E-UTRA carrier RSSI) (i.e., E-UTRA carrier RSSI vs N×RSRP),where N is the number of RB's of the E-UTRA carrier RSSI measurementbandwidth. The measurements in the numerator and denominator shall bemade over the same set of resource blocks.

E-UTRA Carrier Received Signal Strength Indicator (RSSI) may include thelinear average of the total received power (in [W]) observed only inOFDM symbols containing reference symbols for antenna port 0, in themeasurement bandwidth, over N number of resource blocks by the UE fromall sources (including co-channel serving and non-serving cells),channel interference, thermal noise, and the like. In the case thathigher layer signaling indicates certain subframes for performing RSRQmeasurements, the RSSI may be measured over all OFDM symbols in theindicated subframes.

The reference point for the RSRQ shall be the antenna connector of theUE.

In the case that receiver diversity is in use by the UE, the reportedvalue shall not be lower than the corresponding RSRQ of any of theindividual diversity branches.

3) [RSSI]

RSSI may correspond to the received wide band power including thermalnoise and noise generated in a receiver within the bandwidth defined bythe receiver pulse shaping filter.

The reference point for the measurement shall be the antenna connectorof the UE.

In the case that receiver diversity is in use by the UE, the reportedvalue shall not be lower than the corresponding UTRA carrier RSSI of anyof the individual received antenna branches.

According to the definition, a UE operating in the LTE system may beallowed to measure RSRP in a bandwidth corresponding to one of 6, 15,25, 50, 75, and 100 RB (resource block), through information element(IE) in relation to a measurement bandwidth transmitted in systeminformation block type 3 (SIB3) in the case of an Intra-frequencymeasurement, and through an allowed measurement bandwidth transmitted insystem information block type 5 (SIBS) in the case of an Inter-frequencymeasurement. Alternatively, in the case that the IE is not existed, theUE may measure in a frequency band of the whole DL system as default. Atthis time, in the case that the UE receives the allowed measurementbandwidth, the UE may regard the corresponding value as the maximummeasurement bandwidth and may measure RSRP value freely within thecorresponding bandwidth/value. However, in order for a serving cell totransmit the IE defined as wideband (WB)-RSRQ and configure the allowedmeasurement bandwidth to be 50 RBs or more, the UE shall calculate theRSRP value for the whole allowed measurement bandwidth. Meanwhile, theRSSI may be measured in the frequency band that a receiver of the UE hasaccording to the definition of the RSSI bandwidth.

FIG. 17 illustrates a panel antenna array to which the present inventionmay be applied.

Referring to FIG. 17, a panel antenna array includes Mg number of panelsin a horizontal domain and Ng number of panels in a vertical domain, andone panel may include M columns and N rows. Particularly, in thisdrawing, a panel is shown based on cross polarization (X-pol) antenna.Accordingly, the total number of antenna elements may be 2*M*N*Mg*Ng.

Method for Transmitting and Receiving Channel State Information

In the #89 conference of 3GPP RAN1 working group, it is agreed that theDL codebook configuration scheme follows R1-1709232 (“WF on Type I andII CSI codebooks”). In this document, it is described Type I codebookconfiguration scheme corresponding to a single panel (SP) (i.e., Type Isingle-panel codebook) having normal resolution and a multi panel (MP)(i.e., Type I multi-panel codebook) and Type II codebook configurationscheme based on linear combination.

Hereinafter, the codebook described in the present disclosure mayinclude a codebook agreed to follow R1-1709232 (“WF on Type I and II CSIcodebooks”) and a codebook that may be configured with the similarprinciple.

In the present invention, in the case of using the codebook describedabove, hereinafter, a codebook subset restriction (CSR) method isproposed for the purpose of interference control between neighboringcells, mainly. The CSR means that an eNB restricts use of a specificprecoder (i.e., specific PMI or specific beam) with respect to aspecific UE. That is, a UE is restricted to report PMI, RI, PTI, and thelike that correspond to one or more precoder (i.e., precoder codebooksubset) which are specified by a CSR bitmap configured by an eNB. TheCSR may be configured with a bitmap that indicates a specificprecoder(s) (i.e., PMI) for each of different ranks in which a reportingof PMI, RI, PTI, and the like from a UE is restricted.

Hereinafter, in the description of the present invention, an antennaport in the text may be mapped to an antenna element according tovirtualization of a TXRU, and is commonly called as a ‘port’ for theconvenience of description.

Hereinafter, in the description of the present invention, it isdescribed that 1-dimension/domain is referred to as horizontaldimension/domain mainly, and 2-dimension/domain is referred to asvertical dimension/domain mainly, in 2D antenna array, but the presentinvention is not limited thereto.

In addition, hereinafter, in the description of the present invention,unless otherwise described, the same variables used in each Equation maybe represented by the same symbols, and also interpreted in the samemanner.

Furthermore, hereinafter, in the description of the present invention, abeam may be interpreted as a precoding matrix (or precoding vector orcodeword) for generating the corresponding beam, and a beam group may beinterpreted as the same meaning as a set of precoding matrixes (or a setof precoding vectors).

The codebook subset restriction (CSR) supported in LTE is defined inClass A codebook of the similar property to Type I codebook.

This may be indicated to a UE as a bitmap configured for each beamindex+rank (N1*O1*N2*O2+8) and for each W2 index (codebook config 1:4(bit)+4(bit)+2(bit)+2(bit)/codebook config 2-4:16(bit)+16(bit)+16(bit)+8(bit)). That is, each of the bits configuring abitmap indicating the CSR is in relation to a codebook index and/or aprecoder for a specific layer. In the case that a codebook index isconfigured with i_1 (a first PMI, W1) and i_2 (a second PMI, W2), thebitmap for indicating the CSR may include bits related to a precoder forcodebook index i_1 (a first PMI, W1) and/or a specific layer and bitsrelated to a precoder for codebook index i_2 (a second PMI, W2) and/or aspecific layer.

That is, when an index for a specific (multiple) codebook beam(precoder) is transmitted from an eNB as a bitmap (i.e., in a bitmap,when a bit value corresponding to an index for a specific (multiple)codebook beam (precoder) is zero), the UE does not consider the codebookused by the beam (precoder) when performing a CSI reporting (feedback)(i.e., reporting of PMI, RI, PTI, etc. corresponding to a specific beam(precoder) is restricted). In addition, the UE also does not report aspecific rank transmitted to the CSR for each rank when performing a CSIfeedback.

Here, N1 is the number of first domain (dimension) antenna ports, N2 issecond domain (dimension) antenna ports, o1 is a first domain(dimension) oversampling factor and o2 is a second domain (dimension)oversampling factor.

[Type I Codebook]

Embodiment 1: In Type 1 SP (Single Panel) codebook, when configuring acodebook of a UE configured with 16-port or more, the CSR for twointer-group co-phase {e.g., 1, exp(j*1pi/4), exp(j*2pi/4), exp(j*3pi/4)and/or exp(j*pi/4), exp(j*3pi/4), exp(j*5pi/4), exp(j*7pi/4)} componentsfor each of an identical polarization may be configured/applied. Herein,exp( ) means an exponential function, j means a unit of imaginary numberand pi means π.

In 16-port or more of SP Type 1 codebook, rank 3-4 codebook isconfigured with 2 Dimensional (2D) (or 1 Dimensional (1D)) DiscreteFourier Transform (DFT) Grid of Beam (GoB) which is divided into twoantenna port groups for each of an identical polarization in asingle-panel.

That is, each antenna port group includes DFT beams having(N1*N2/2)-length (in a single antenna port group, N1*N2/2 DFT beams(precoder) are included). Each of the beam (precoder) may be representedas

$b_{i} \in {{C^{\frac{N_{1}N_{2}}{2} \times 1}( {{i = 0},1,{{\ldots\mspace{14mu}\frac{N_{1}N_{2}O_{1}O_{2}}{2}} - 1}} )}.}$

The final precoding beam (precoding matrix) for an identicalpolarization is represented as

$v_{i} = {\begin{bmatrix}b_{i} \\{c_{i}b_{i}}\end{bmatrix}.}$

Here, c₁ is {1, exp(j*1pi/4), exp(j*2pi/4), exp(j*3pi/4)} value.

Accordingly, the number of beams represented in rank 3-4 of 16 port ormore is

${\frac{N_{1}N_{2}O_{1}O_{2}}{2}*4} = {2N_{1}N_{2}O_{1}{O_{2}.}}$

Accordingly, a bitmap size is determined as

${bitmap\_ size} = \{ {\begin{matrix}{2N_{1}N_{2}O_{1}O_{2}} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{N_{1}N_{2}O_{1}O_{2}} & {otherwise}\end{matrix}.} $

As such, there is a problem that a bit size for performing the CSR ischanged for each beam according to a rank.

In order to solve the problem, the following alternatives (Alts) may beconsidered.

In addition, as shown in the example above, in the case that inter-groupco-phase of {1, exp(j*1pi/4), exp(j*2pi/4), exp(j*3pi/4), exp(j*pi/4),exp(j*3pi/4), exp(j*5pi/4), exp(j*7pi/4)} is used, a bitmap may be usedof which size is

${bitmap\_ size} = \{ {\begin{matrix}{3N_{1}N_{2}O_{1}O_{2}} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{N_{1}N_{2}O_{1}O_{2}} & {otherwise}\end{matrix}.} $

Alt. 1: Accordingly, the CSR for each beam may be defined as a bitmap of3N₁N₂O₁O₂ (N₁N₂O₁O₂+2N₁N₂O₁O₂) (the number of states of c_(i) is 4) or4N₁N₂O₁O₂(N₁N₂O₁O₂+3N₁N₂O₁O₂) (the number of states of c_(i) is 8). Inaddition, 8-bitmap for each rank is used, and the CSR for each beam andthe CSR for each rank may be encoded independently or integrally.

Alt. 2: Alternatively, the CSR for each beam may be separately definedfor each rank, and the CSR may be configured such that the rank groupthat shares the same beam group is distinguished with 1 bit indicator.Accordingly, a bitmap size may be

${bitmap\_ size} = \{ {{\begin{matrix}{1 + {2N_{1}N_{2}O_{1}O_{2}} + 2} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{1 + {N_{1}N_{2}O_{1}O_{2}} + 6} & {otherwise}\end{matrix}{or}{bitmap\_ size}} = \{ {\begin{matrix}{1 + {3N_{1}N_{2}O_{1}O_{2}} + 2} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{1 + {N_{1}N_{2}O_{1}O_{2}} + 6} & {otherwise}\end{matrix}.} } $

In Alt. 2 above, 1 bit of the first term is an indicator fordistinguishing different ranks from rank 3-4 (e.g., rank 3-4 isindicated when a bitmap value is ‘0’, and other ranks are indicated whena bitmap value is ‘1’). The second term is a coefficient of a beam usedfor each rank group. The third term is the number of ranks in each rankgroup, 2 is a bit number for distinguishing ranks 3, 4 and 6 is a bitnumber for distinguishing ranks 1, 2, 5, 6, 7 and 8.

In order to reduce signaling overhead for a bitmap for each rank, a sizeof bitmap for each rank may be configured based on a capabilityreporting of UE. For example, in the case that a UE is able to processup to 4 layer, the size of bitmap for each rank is 4, and in the case ofAlt. 2, a bitmap size may be

${bitmap\_ size} = \{ {\begin{matrix}{1 + {2N_{1}N_{2}O_{1}O_{2}} + 2} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{1 + {N_{1}N_{2}O_{1}O_{2}} + 2} & {{for}\mspace{14mu}{rank}\mspace{14mu} 1\mspace{14mu}{and}\mspace{14mu} 2}\end{matrix}.} $

Hereinafter, for the alternative described below, a CSR bit sizeallocation according to capability reporting of UE may also beextendedly applied apparently.

Alternatively, except the group-cophase, it may be configured that onlyDFT beam is restricted such as

${bitmap\_ size} = \{ {\begin{matrix}{N_{1}N_{2}O_{1}{O_{2}/2}} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{N_{1}N_{2}O_{1}O_{2}} & {otherwise}\end{matrix}.} $

Alt. 2-1: The CSR for rank 3-4 may be indicated by the union of a bitmapof an index for each beam (precoder) and a bitmap of panel co-phaseindex (i.e., concatenation of two bitmaps), and a UE may not report thebeam to which the corresponding CSR is configured and the co-phase indexwhen performing a CSI feedback. Accordingly, a bitmap size is

${bitmap\_ size} = \{ {\begin{matrix}{1 + {\frac{1}{2}N_{1}N_{2}O_{1}O_{2}} + 4 + 2} & {{for}\mspace{14mu}{rank}\mspace{14mu} 3\mspace{14mu}{and}\mspace{14mu} 4} \\{1 + {N_{1}N_{2}O_{1}O_{2}} + 6} & {otherwise}\end{matrix}.} $

In Alt. 2-1, in rank 3 and 4, the second and the third terms ½N₁N₂O₁O₂+4is the number of beams (b_(i)), and herein, 4 (bit) corresponds tobitmap for inter-panel co-phase.

The case of Alt. 2-1, in comparison with other alternatives, there is anadvantage that feedback overhead for rank 3-4 may be significantlyreduced.

As another scheme, except for group-cophase, by configuring onebit-field corresponding to all ranks, a beam restriction (i.e., CSR) maybe performed. That is, CSR bit-field of Type I CSI may be provided withN₁N₂O₁O₂, the DFT-beam for all ranks may be CSR. In other words, abitmap of N₁N₂O₁O₂ length for CSR indication may be commonly applied toall ranks without regard to a rank.

However, for rank 3-4, a problem occurs for applying N₁N₂O₁O₂/2efficiently. In order to solve the problem, Type I codebook will bedescribed first.

Equation 15 below exemplifies Type I codebook.

$\begin{matrix}{{\varphi_{n} = e^{j\;\pi\;{n/2}}}{\theta_{p} = e^{j\;\pi\;{p/4}}}u_{m} = \{ {{\begin{matrix}\lbrack {1\mspace{14mu} e^{j\frac{2\;\pi\; m}{O_{2}N_{2}}\mspace{14mu}\ldots\mspace{14mu} e^{j\frac{2\;\pi\;{m{({N_{2} - 1})}}}{O_{2}N_{2}}}}} \rbrack & {N_{2} > 1} \\1 & {N_{2} = 1}\end{matrix}v_{l,m}} = {{\lbrack {u_{m}\mspace{14mu}{e^{j\frac{2\;\pi\; l}{O_{1}N_{1}}}}_{u_{m}}\mspace{14mu}\ldots\mspace{14mu}{e^{j\frac{2\;\pi\;{l{({N_{1} - 1})}}}{O_{1}N_{1}}}}_{u_{m}}} \rbrack^{T}{\overset{\sim}{v}}_{l^{\prime},m}} = \lbrack {u_{m}\mspace{11mu}{e^{j\frac{4\pi\; l^{\prime}}{O_{1}N_{1}}}}_{u_{m}}\mspace{14mu}\ldots\mspace{14mu}{e^{j\frac{4\pi\;{l^{\prime}{({{N_{1}/2} - 1})}}}{O_{1}N_{1}}}}_{u_{m}}} \rbrack^{T}}} } & \lbrack {{Equation}\mspace{14mu} 15} \rbrack\end{matrix}$

In Equation 15, φ_(n)=e^(jπn/2), θ_(p)=e^(jπp/4) is group-cophase forcodebook configuration for rank 3 and 4, respectively. u_(m) denotes aDFT vector of N2 domain, {tilde over (v)}_(l′,m) denotes a DFT vector ofN1 domain in rank 3-4, and v_(l,m) denotes a DFT vector of N1 domainexcept rank 3-4.

In describing mathematical expressions for {tilde over (v)}_(l′,m) andv_(l,m) when l value of v_(l,m) is even number, from the first term ofv_(l,m), N1N2/2^(th) element includes {tilde over (v)}_(l′,m).

Accordingly, in the case that the CSR is performed by v_(l,m), wherel=0, . . . , O₁N₁−1, m=0, . . . , O₂N₂−1 as a bit-field of N₁O₁N₂O₂,when the even number of DFT beams in N1 domain is restricted, the DFTbeam in N1 domain corresponding to

${{{\overset{\sim}{v}}_{l^{\prime}}}_{,m} = 0},1,{{\ldots\mspace{14mu}\frac{N_{1}O_{1}}{2}} - 1}$

that corresponds 3-4 may be restricted simultaneously. In other words,when v_(2i,m) is restricted, a UE may interpret that {tilde over(v)}_(i,m) is restricted.

FIG. 18 illustrates an antenna pattern gain when the codebook subsetrestriction is applied according to an embodiment of the presentinvention.

In FIG. 18, the antenna pattern gain of 32-port (N1=16, N2=1) isexemplified. FIG. 18 shows the case of l₁=l, l₂=l′.

Referring to FIG. 18, bold lines (1801, 1802 and 1803) representv_(i,m), and fine lines (1811, 1812 and 1813) represent {tilde over(v)}_(l′,m).

As shown in FIG. 18, since the number of ports of v_(l,m) is two timesof {tilde over (v)}_(l′,m), 3 dB beam width is about a half, and owingto this, the beam of v_(l,m) corresponding to odd number l value islocated between two neighboring v_(l′,m) beams.

For example, v_(l) ₁ _(−1,m) is located between beams of {tilde over(v)}_(l) ₁ _(−1,m), {tilde over (v)}_(l) ₂ _(,m). Accordingly, whenv_(l,m) corresponding to odd number l=2i+1 value is restricted, it maybe predefined (or promised between an eNB and a UE) that two beamscorresponding to {tilde over (v)}_(i,m) and {tilde over (v)}_(i+1,m) arerestricted simultaneously. And/or, as the same way as the proposalabove, when v_(2i,m) corresponding even number l=2i value is restricted,a UE may interpret that {tilde over (v)}_(i,m) is restricted. In thiscase, since a specific beam may be restricted twice simultaneouslydepending on l value, a UE may interpret that the corresponding {tildeover (v)}_(i,m) is restricted when {tilde over (v)}_(i,m) is restrictedone or more times with v_(l,m).

In other words, except for the case that the number of antenna ports fortransmitting CSI-RS is 16 or more and the number of layers (or ranks)(associated with the RI that a UE reports in the CSI) is 3 or 4, a bitof N₁N₂O₁O₂ bitmap is associated with each precoder. Referring to FIG.18, a first beam (precoder) 1801, a second beam (precoder) 1802 and athird beam (precoder) 1803 are associated with one bit of bitmap ofN₁N₂O₁O₂, respectively. Accordingly, when the CSR is indicated in aspecific bit (e.g., a specific bit value is ‘0’), a reporting of the PMIcorresponding to the beam (precoder) which is associated with thecorresponding bit is not allowed (restricted).

On the contrary, in the case that the number of antenna ports fortransmitting CSI-RS is 16 or more and the number of layers (or ranks)(associated with the RI that a UE reports in the CSI) is 3 or 4,multiple bits of N₁N₂O₁O₂ bitmap may be associated with each precoder.Referring to FIG. 18, in the case that the number of antenna ports fortransmitting CSI-RS is 16 or more and the number of layers (or ranks) is3 or 4, each of three bits may be associated with each beam (precoder)1811, 1812 and 1813. For example, except for the case that the number ofantenna ports for transmitting CSI-RS is 16 or more and the number oflayers (or ranks) is 3 or 4, three bits of the bit associated with thefirst beam (precoder) 1801, the bit associated with the second beam(precoder) 1802 and the bit associated with the third beam (precoder)1803 may be associated with the fifth beam (precoder) 1812, when thenumber of antenna ports for transmitting CSI-RS is 16 or more and thenumber of layers (or ranks) is 3 or 4. According to this method, the bitassociated with the first beam (precoder) 1801 may also be associatedwith the fourth beam (precoder) 1811, and also associated with the fifthbeam (precoder) 1812. Accordingly, when the CSR is indicated in the bitassociated with the first beam (precoder) 1801 (e.g., when thecorresponding bit value is ‘0’), the CSR may be applied to both of thefourth beam (precoder) 1811 and the fifth beam (precoder) 1812. That is,as described above, when v_(l,m) corresponding to odd value l=2i+1 isrestricted, two beams corresponding to {tilde over (v)}_(i,m) and {tildeover (v)}_(i+1,m) may be restricted simultaneously.

In addition, as described above, depending on l value, a specific beammay be restricted twice simultaneously. That is, even in the case thatv_(l,m) corresponding to odd value l=2i+1 is restricted and also, in thecase that v_(l,m corresponding to odd value l=)2i+1 is restricted,{tilde over (v)}_(i,m) may be restricted. Referring to FIG. 18, sincethe bit associated with the first beam (precoder) 1801, the bitassociated with the second beam (precoder) 1802 and the bit associatedwith the third beam (precoder) 1803 may be associated with one fifthbeam (precoder) 1812, when the CSR is indicated to any one bit of thebit associated with the first beam (precoder) 1801, the bit associatedwith the second beam (precoder) 1802 and the bit associated with thethird beam (precoder) 1803 (e.g., when bit value is ‘0’), the CSR mayalso be applied to the fifth beam (precoder) 1812.

Furthermore, as described above, in the description of FIG. 18 above, inthe case that the number of antenna ports for transmitting CSI-RS is 16or more and the number of layers (or ranks) is 3 or 4, multiple bits mayinclude three bits. At this time, indexes of the three bits may have amultiple relation of a specific number (e.g., N_2*O_2). At this time,the bits belong to a bitmap for CSR configuration may be indexedsequentially from zero, from LSB (Most Significant Bit) to MSB (MostSignificant Bit).

In addition, as described above, for example, v_(l) ₁ _(−1,m) is locatedbetween beams of {tilde over (v)}_(l) ₂ _(−1,m), {tilde over (v)}_(l) ₂_(,m). Accordingly, when v_(l,m) corresponding to odd number l=2i+lvalue is restricted, it may be predefined (or promised between an eNBand a UE) that two beams corresponding to {tilde over (v)}_(i,m) and{tilde over (v)}_(i+1,m) are restricted simultaneously. And/or, as thesame way as the proposal above, when v_(2i,m) corresponding even numberl=2i value is restricted, a UE may interpret that {tilde over (v)}_(i,m)is restricted. In other words, the bits in the bitmap for CSRconfiguration may belong to one or multiple bit units. For example, inthe bitmap constructed by a_n, . . . , a_0, a_40 may belong to both ofmultiple bit units constructed by (a_24, a_32, a_40) and multiple bitunits constructed by (a_40, a_48, a_56). In addition, a_48 may belong tomultiple bit units constructed by (a_40, a_48, a_56). Accordingly, whenthe CSR is indicated to either one of bit in the bitmap for CSRconfiguration, depending on whether the multiple bit units to which thisbit belongs is 1 or multiple numbers, a reporting of the PMIcorresponding to a single precoder may be restricted (in the case that{tilde over (v)}_(i,m) is restricted when v_(2i,m) corresponding to evennumber l=2i value is restricted) or a reporting of the PMI correspondingto multiple precoders may be restricted (in the case that two beamscorresponding to {tilde over (v)}_(i,m) and {tilde over (v)}_(i+1,m) arerestricted when v_(l,m) corresponding to odd number l=2i+1 value isrestricted).

Alternatively, it may be predefined (or promised between an eNB and aUE) that only either specific one (e.g., {tilde over (v)}_(i,m)) of twobeams corresponding to {tilde over (v)}_(i,m) and {tilde over(v)}_(i+1,m) is restricted when v_(i,m) corresponding to odd numberl=2i+1 value is restricted. As described above, in the example describedabove, when the CSR is indicated to the bit associated with the firstbeam (precoder) 1801 (e.g., when the corresponding bit value is ‘0’),the CSR may be applied to either one of beam (precoder) among the fourthbeam (precoder) 1811 and the fifth beam (precoder) 1812, which isassociated with the corresponding bit. At this time, it may be informedto a UE by higher layer signaling (e.g., RRC signaling) on which beambetween {tilde over (v)}_(i,m) and {tilde over (v)}_(i+1,m) isrestricted. In other words, in the example of FIG. 18, in the case thatthe number of antenna ports for transmitting CSI-RS is 16 or more andthe number of layers (or ranks) is 3 or 4, each of three bits may beassociated with the fourth beam (precoder) 1811, the fifth beam(precoder) 1812 and the sixth beam (precoder) 1813. At this time, onlywhen the CSR is indicated in a specific bit among three bits, areporting of the PMI corresponding to the beam (precoder) associatedwith it may be restricted.

Alternatively, when v_(i,m) corresponding to odd number l=2i+1 value isrestricted, it may be predefined (or promised between an eNB and a UE)that a beam in which {tilde over (v)}_(l′,m) is coupled with a specificθ_(p)=e^(jπp/4) is restricted. It is predefined (or promised between aneNB and a UE) that [{tilde over (v)}_(l′,m) θ_(p){tilde over(v)}_(l′,m)] is restricted, and an eNB may inform θ_(p)=e^(jπp/4) to aUE by higher layer signaling (e.g., RRC signaling) or inform to a UE bya separate bitmap from the CSR.

Embodiment 2: When configuring a codebook of a UE configured with MultiPanels (MP) codebook, the CSR for inter-panel co-phase (e.g.,{1,j,−1,−j} and/or {exp(j*pi/4), exp(j*3pi/4), exp(j*5pi/4),exp(j*7pi/4)} and/or {exp(j*pi/4), exp(j*3pi/4), exp(j*5pi/4),exp(j*7pi/4)}*{exp(−j*pi/4), exp(j*pi/4)}) element for each polarizationmay be configured/applied.

Type 1 multi panel (MP) codebook is identically configured/applied foreach panel with a single pattern codebook, and configured with acodebook to which inter-panel co-phase is added. Herein, Ng is thenumber of panel, N1 and N2 are the number of antenna ports of a firstdomain and a second domain in a panel, respectively. Accordingly, eachpanel includes N₁N₂O₁O₂ number of 2D or 1D DFT beams and in the case ofconsidering all of panel co-phase, a length of precoding beam for eachpolarization is Ng*N1*N2.

For panel co-phase, according to the mode defined in R1-1709232 (“WF onType I and II CSI codebooks”), in the case of mode 1 (panel co-phase {1,j, −1, −j} only for Wide Band (WB)), by using co-phase of 4 states, thenumber of final precoding beams becomes 4^((N) ^(g) ⁻¹⁾N₁N₂O₁O₂. Inaddition, a bitmap size of CSR for each beam using this becomes 4^((N)^(g) ⁻¹⁾N₁N₂O₁O₂. In the case of mode 2 (WB+Sub-Band (SB) panelco-phase), panel co-phase with WB is independently performed forpolarization, and there may be more number of total WE codebooks, butthe number of final DFT beams for each polarization is the same as4^((N) ^(g) ⁻¹⁾N₁N₂O₁O₂. Accordingly, for MP codebook, the CSR of WBbeam for each polarization and the CSR for each rank may be configuredwith a bitmap of 4^((N) ^(g) ⁻¹⁾N₁N₂O₁O₂+4 regardless of mode, and abeam and a rank may be configured with independent field similar toembodiment 1 described above.

Embodiment 2-1: Panel common DFT beam and panel co-phase may beconfigured with separate CSR fields.

Since the number of 4^((N) ^(g) ⁻¹⁾N₁N₂O₁O₂ may becomes significantlyincreased according to Ng value, a bitmap of N₁N₂O₁O₂+4 may beconfigured by configuring the CSR for a beam index and the CSR field forco-phase separately. In this case, a UE operates such that final WBprecoding beam for each polarization corresponding to union of twofields is not reported when performing CSI feedback. In embodiment 2-1described above, a beam (final Ng*N1*N2-length beam)+CSR for each rankmay be performed, and a beam and a rank may be configured withindependent fields similar to embodiment 1 described above.

Embodiment 2-2: The CSR for each beam may be configured by consideringpanel-common DFT beam, and WB co-phase and SB co-phase.

Considering SB panel co-phase in MP codebook mode 2 additionally, totalbitmap size of the final Ng*N1*N2-length precoding beam for eachpolarization configured based on DFT becomes 4^((N) ^(g) ⁻¹⁾2^((N) ^(g)⁻¹⁾N₁N₂O₁O₂, and the UE configured with MP mode 2 performs the CSR foreach beam using bitmap of 4^((N) ^(g) ⁻¹⁾2^((N) ^(g) ⁻¹⁾N₁N₂O₁O₂ orperforms the CSR for each beam+rank using bitmap of 4^((N) ^(g)⁻¹⁾2^((N) ^(g) ⁻¹⁾N₁N₂O₁O₂+4.

Embodiment 2-2-1: The panel-common DFT beam, and WB co-phase and SBco-phase may be configured with an independent CSR field.

Similar to embodiment 2-1 described above, as Ng increases, since a sizeof total bitmap increases significantly, in order to prevent it, byconfiguring CSR with separate fields of the panel-common DFT beam, andWB co-phase and SB co-phase, bitmap CSR of N₁N₂O₁O₂+4+2 may beperformed. Here, ‘4’ represents a state of WB co-phase and ‘2’represents a state of SB co-phase. In this case, a UE operates so as notto report the final precoding beam for each polarization thatcorresponds to the union of three fields when performing CSI feedback.

The embodiment described above may be apparently extended to the casethat a beam selection (codebook selection) is applied independentlybetween panels.

Embodiment 3: Multiple codebook configuration factors are existed (e.g.,W1 index and W2 index of dual stage codebook), and when theseconfiguration factors are configured with different CSR fields, an eNBmay inform whether the CSR is configured with the union or theintersection of these CSR fields to a UE with 1 bit indicator.

The dual stage codebook may be configured with different fields for thepurpose of reducing overhead of the codebook factor (e.g., beam index)corresponding to W1 and the codebook factor (e.g., beam selector and/orco-phase) corresponding to W2. In this case, when two fields are down toa UE simultaneously, the existing UE operates so as not to report thecodebook index that corresponds to the union indicated by the two fieldswhen performing CSI feedback. However, when a UE operates with the uniononly, since the codebook constituent elements may be restrictedaggressively, actual performance of UE may be degraded.

In order to prevent such a problem, as a method for informing only theelements that require the CSR to a UE in pin-point manner, the CSR maybe performed with an intersection of multiple CSR fields. Accordingly,when an eNB informs multiple CSR fields to a UE, the eNB may informwhether the CSR is performed with the union or the intersection of thesefields to a UE with 1 bit indicator. Alternatively, an eNB may inform aninterpretation of multiple CSR fields to a UE by using a bitmap to whichbits (K-bits) is allocated as much as the multiple number (K number) offields.

[Type II Codebook]

Type II codebook is configured by linearly combining (LC) selected theDFT beams of 2D or 1D L (L=2, 3 and 4) DFT beams which are orthogonalwith independent amplitude and coefficient of phase for each layer foreach polarization, respectively. Accordingly, for the factor that may beused for the purpose of controlling inter-cell interference among theelements of the LC codebook, the number (N₁N₂O₁O₂) of DFT beams and thecoefficient (size/phase) of each beam which are linearly combined.

Among the linearly combined beams, in the case that one or multiplebeam(s) indicated by the CSR is (are) selected among the (2L) candidatesof the beams which are linearly combined, with respect to thecorresponding beam(s), a UE may configure a codebook byconfiguring/applying zero for amplitude coefficients always. In the casethat power control is performed by turning on/off the beams indicated bythe CSR for the purpose of interference management and the like, thereis an effect of preventing interference perfectly. However, the UE thatreports the corresponding beam with the most preferred beam is unable toselect the corresponding beam, and accordingly, the performance may bedegraded.

Embodiment 4: The index of linearly combined beam(s) and/or the degreeof power-level of the corresponding beam(s) (e.g., amplitudecoefficient) may be indicated with the CSR.

In embodiment 4, for the purpose of soft power control for inter-cellinterference, the index of linearly combined beam(s) and/or the degreeof power-level (e.g., amplitude coefficient) are indicated with the CSR.In the case that N₁N₂O₁O₂ DFT beams configuring the LC codebook areexisted and the number of amplitude power coefficients are defined asSA, the CSR may be indicated by using the bitmap of N₁N₂O₁O₂+SA orS_(A)N₁N₂O₁, similar to embodiments 1, 2 and 3. The former case has anadvantage that there is great effect of signal overhead saving.Alternatively, only the maximum allowed power level may be indicated,and in this case, overhead may be reduced by using the indicator of┌log₂ S_(A)┐-bit, not a bitmap.

Embodiment 4 described above may also be used for Type I codebook aswell as Type II codebook, and used in the process of computing the bestpreferred PMI, and accordingly, the CSI (e.g., RI, PMI, CQI, CSI-RSresource indicator (CRI), etc.) may be computed.

Embodiment 5: In the case that beamforming (e.g., analog and/or digital)is performed for each port or port group like class B of LTE, the CSRmay be indicated by using the bitmap of M (e. g, M=N₁N₂,# of port orport group).

This embodiment may be applied to the case of using the CSI-RS to whichbeamforming (e.g., analog and/or digital) for each port or port group isapplied like class B of LTE, and the CSR may be indicated to an eNBusing the bitmap using M bits or M+R bits (here, R is the maximum rank)for the CSR for each port.

In addition, in the case of embodiment 5, in combination with embodiment4 described above, the CSR for the purpose of soft power control foreach port may be performed. In the case that multiple number (K) ofCSI-RS resources is indicated, a bitmap may be extendedly applied to KMor K+M. In the case of KM, whereas it is easy to indicate with the CSRin pin-point manner among total KM ports, overload is great. And in thecase of K+M, whereas overload is reduced, the number of ports that needsto be applied with the CSR becomes greater excessively.

Such CSR information may be indicated for each CSI process by beingincluded in CSI-RS resource setting or indicated to a UE by separatehigher layer signaling (e.g., RRC signaling).

In the case that the case of LC codebook (R1-1709232) applied in abeamformed CSI-RS described below is used, embodiment 5 and embodiment 4described above may be combined and applied. That is, the CSR may beperformed in combination or independently of combining amplitudecoefficients coupled with the part for port-group or port selection.

The LC codebook applied in the beamformed CSI-RS will be described.

In NR, it is supported an extension of Type II Category (Cat) 1 CSI forranks 1 and 2 like Equation 16 below.

$\begin{matrix}{w_{1} = \begin{bmatrix}E_{\frac{X}{2} \times L} & 0 \\0 & E_{\frac{X}{2} \times L}\end{bmatrix}} & {{Equation}\mspace{14mu} 16}\end{matrix}$

In Equation 16, X is the number of CSI-RS port(s). L value may beconfigurable (L□{2, 3, 4}).

Available value of X follows Type II SP codebook as represented inEquation 17 below.

$\begin{matrix}{E_{\frac{X}{2} \times L} = {\quad\lbrack {{e^{(\frac{X}{2})}}_{{mod}{({{md}\frac{X}{2}})}}{e^{(\frac{X}{2})}}_{{mod}{({{md} + {1\frac{X}{2}}})}}\mspace{14mu}\ldots\mspace{14mu}{e^{(\frac{X}{2})}}_{{mod}{({{{md} + L - 1},\frac{X}{2}})}}} \rbrack}} & {{Equation}\mspace{14mu} 17}\end{matrix}$

In Equation 17,

$e^{(\frac{X}{2})}i$

is a vector of which length is

$\frac{X}{2},$

of which ith component is 1 and other components are 0. The portselection m value is determined within

${m \in \{ {0,1,\ldots\mspace{14mu},{\lbrack \frac{X}{2d} \rbrack - 1}} \}},$

Wide Band

$\lbrack {\log_{2}( \frac{X}{2d} )} \rbrack$

bit is used for a computation and a reporting of m. Value of d may beconfigurable (d□{1, 2, 3, 4} under the condition of

$ {d \leq {\frac{X}{2}\mspace{14mu}{and}\mspace{14mu} d} \leq L} ).$

The amplitude scaling and the phase combining coefficients follow TypeII SP codebook together with these configurations.

Embodiment 6: In the case that a bit-width of the codebook generated asa result in the multiple CSR fields (e.g., W1 index, RI, W2 index andDFT beam index) indicated with the CSR may be decreased, for thecorresponding CSI feedback, CSI may be reported by remapping an indexwith the decreased bit-width.

For example, a rank indicator is described. In the case that a UEreports that the UE may report rank 8 with the capability and 8-bit rankCSR bitmap (i.e., bitmap for rank restriction configuration) isindicated with “00001111” (here, it is assumed that ‘0’ means no CSR and‘1’ means CSR, and bits correspond rank 1, . . . , 8 from the mostsignificant bit sequentially), the UE maps RI with 2 bits, not 3 bits,and feedback overhead may be reduced. That is, since the number of RIsin which a reporting is allowed in rank CSR bitmap “00001111” is 4(there are four ‘0’ values in the above example), the bit-width for RIreporting may be determined with 2 bits, and accordingly, RI feedbackoverhead may be reduced.

As another example, it is assumed that W2 index CSR bitmap ofconfiguration (config) 2 rank 1 is configured with “0101” andcorresponds to 1, j, −1, −j from the most significant bit. In this case,in the case that a preferred PMI of a UE is rank 1, for W2, SB CSIfeedback may be reported with 1 bit co-phase, not 2 bits. In the 1 bitco-phase, an eNB and a UE may interpret that “0” state of 1 bit isremapped to ‘1’ and “1” state is remapped to ‘−1’.

FIG. 19 is a diagram illustrating a method for transmitting andreceiving channel state information according to an embodiment of thepresent invention.

Referring to FIG. 19, a UE receives codebook configuration informationfrom an eNB (step, S1901).

Here, the codebook configuration information may include a bitmap forCSR configuration and/or a bitmap for rank restriction configuration.

The bitmap for CSR configuration and/or the bitmap for rank restrictionconfiguration may be configured according to the embodiments of thepresent invention described above.

For example, the bitmap for CSR configuration may use different bitfields (i.e., bitmaps configured with different bit-widths) for the casethat the number of antenna configured to a UE is 16 or more (e.g., 16,24, 32, 64, etc.) and the number of layers (or rank) (this is associatedwith the RI reported in CSI) is 3 or 4, and for the case otherwise,respectively.

Alternatively, the bitmap for configuring the CSR is commonly appliedwithout regard to the number (this is associated with the RI reported inCSI) of layers associated with the rank indicator (RI) in the CSI.Without regard to the number of antenna ports configured to a UE and/orthe number (this is associated with the RI reported in CSI) of layers, acommon bit field (i.e., a single bitmap) may be used. As such, in thecase that a common bitmap is used without regard to the number of layers(or ranks), as described above, since the antenna ports of a singlepanel is distinguished by 2 when the number of layers (or ranks) of 16ports or more is 3 or 4, even in the case that the common bitmap isused, an application (interpretation) method may be changed depending onthe number of layers (or ranks).

The UE may receive a CSI-RS on one or more antenna ports from the eNB(step, S1902).

In addition, although it is not shown in FIG. 19, the UE may receiveconfiguration information of the number of antenna ports for configuringcodebook from the eNB. That is, the UE may receive each of theinformation for the number (N_1) of first domain antenna ports and thenumber (N_2) of second domain antenna ports. In addition, the number ofCSI-RS antenna ports may be determined according to the number ofantenna ports configured as such.

The UE reports (transmits) the channel state information (CSI) to theeNB (step, S1903).

Here, the UE may compute the CSI by using the CSI-RS received from theeNB. The CSI may include CQI, PMI, CRI, RI, LI (Layer Indication) and/orL1-RSRP.

At this time, according to the embodiments of the present invention, areporting of a specific RI and/or PMI is not allowed for the UEdepending on the bitmap for configuring CSR and/or the bitmap for rankrestriction configuration described above.

Particularly, the reporting of PMI is not allowed, which corresponds toa precoder (or beam) associated with the bit to which CSR is indicatedin the bitmap for configuring CSR. In addition, in the bitmap for rankrestriction configuration, the reporting of RI is not allowed, whichcorresponds to a layer associated with the bit in which rank restrictionis indicated.

For example, as described above, in the case that a common bitmap isused without regard to the number of layers (or ranks) for configuringCSR, interpretation method may be changed depending on the number oflayers (or ranks). In the case that the number of antenna ports isconfigured to be 16 or more and the number of layers (or ranks)associated with the RI in the CSI is 3 or 4, a unit of multiple (e.g.,3) bits in a bitmap for configuring the CSR may be associated with eachprecoder. In addition, in the case that the CSR is indicated in any oneof the multiple bits (e.g., bit value is ‘0’), a reporting of precodingmatrix indicator (PMI) corresponding to the precoder associated with themultiple bits may be not allowed (restricted). On the other hand, exceptthe case that the number of antenna ports is configured as 16 or moreand the number of layers associated with the RI in the CSI is 3 or 4,each bit in the bitmap for configuring the CSR may be associated witheach precoder, and a reporting of PMI corresponding to the precoderassociated with a bit in which the CSR is indicated may not be allowed(restricted) in the CSI.

In addition, as in the description of FIG. 18 above, in the case thatthe number of antenna ports for transmitting CSI-RS is 16 or more andthe number of layers (or ranks) is 3 or 4, multiple bits may includethree bits. At this time, indexes of the three bits may have a multiplerelation of a specific number (e.g., N_2*O_2). At this time, the bitsbelong to a bitmap for CSR configuration may be indexed sequentiallyfrom zero, from LSB (Most Significant Bit) to MSB (Most SignificantBit).

In addition, the bits in the bitmap for CSR configuration may belong toone or multiple bit units. For example, in the bitmap constructed bya_n, . . . , a_0, a_40 may belong to both of multiple bit unitsconstructed by (a_24, a_32, a_40) and multiple bit units constructed by(a_40, a_48, a_56). In addition, a_48 may belong to multiple bit unitsconstructed by (a_40, a_48, a_56). Accordingly, when the CSR isindicated to either one of bit in the bitmap for CSR configuration,depending on whether the multiple bit units to which this bit belongs is1 or multiple numbers, a reporting of the PMI corresponding to a singleprecoder or multiple precoders may be restricted

In addition, according to the above embodiments of the presentinvention, a bit-width of CSI feedback may be flexibly determined basedon the bitmap for configuring CSR and/or the bitmap for configuring rankrestriction. Particularly, a bit-width for reporting the RI in the CSImay be determined depending on a number of RIs (i.e., the number of bitsin which rank restriction is not indicated).

General apparatus to which the present invention may be applied

FIG. 20 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

Referring to FIG. 20, the wireless communication system includes a basestation (eNB) 2010 and a plurality of user equipments (UEs) 2020 locatedwithin the region of the eNB 2010.

The eNB 2010 includes a processor 2011, a memory 2012 and a radiofrequency (RF) unit (or transceiver) 2013. The processor 2011 implementsthe functions, processes and/or methods proposed in FIGS. 1 to 19 above.The layers of wireless interface protocol may be implemented by theprocessor 2011. The memory 2012 is connected to the processor 2011, andstores various types of information for driving the processor 2011. TheRF unit 2013 is connected to the processor 2011, and transmits and/orreceives radio signals.

The UE 2020 includes a processor 2021, a memory 2022 and a radiofrequency (RF) unit (transceiver) 2023. The processor 2021 implementsthe functions, processes and/or methods proposed in FIGS. 1 to 19 above.The layers of wireless interface protocol may be implemented by theprocessor 2021. The memory 2022 is connected to the processor 2021, andstores various types of information for driving the processor 2021. TheRF unit 2023 is connected to the processor 2021, and transmits and/orreceives radio signals.

The memories 2012 and 2022 may be located interior or exterior of theprocessors 2011 and 2021, and may be connected to the processors 2011and 2021 with well known means. In addition, the eNB 2010 and/or the UE2020 may have a single antenna or multiple antennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predeterminedmanner. Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. In addition, some structural elementsand/or features may be combined with one another to constitute theembodiments of the present invention. The order of operations describedin the embodiments of the present invention may be changed. Somestructural elements or features of one embodiment may be included inanother embodiment, or may be replaced with corresponding structuralelements or features of another embodiment. Moreover, it is apparentthat some claims referring to specific claims may be combined withanother claims referring to the other claims other than the specificclaims to constitute the embodiment or add new claims by means ofamendment after the application is filed.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to theembodiments of the present invention may be achieved by one or moreASICs (Application Specific Integrated Circuits), DSPs (Digital SignalProcessors), DSPDs (Digital Signal Processing Devices), PLDs(Programmable Logic Devices), FPGAs (Field Programmable Gate Arrays),processors, controllers, microcontrollers, microprocessors, etc.

In a firmware or software configuration, the embodiments of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in the memory and executed bythe processor. The memory may be located at the interior or exterior ofthe processor and may transmit data to and receive data from theprocessor via various known means.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The present invention, applied to 3GPP 5G (5 generation) system, isprimarily described as an example, but may be applied to variouswireless communication systems in addition to the 3GPP 5G (5 generation)system.

What is claimed is:
 1. A method for transmitting, by a user equipment(UE), channel state information (CSI) in a wireless communicationsystem, the method comprising: receiving first information related torestriction of a rank indicator (RI), wherein the first information isconfigured in a form of a bitmap, and wherein each bit of the bitmapcorresponds to each of layers supported by the UE; and transmitting CSIincluding the RI, wherein a bit width of the RI is determined based onthe first information.
 2. The method of claim 1, wherein the bit widthof the RI is determined based on a number of bits indicating that a RIreporting associated with corresponding layer is allowed.
 3. The methodof claim 2, wherein a bit value ‘0’ indicates that the RI reporting isnot allowed and a bit value ‘1’ indicates that the RI reporting isallowed.
 4. The method of claim 2, wherein values of the RI included inthe CSI are mapped to the bits indicating that the RI reportingassociated with corresponding layer is allowed.
 5. The method of claim2, further comprising: transmitting UE capability information includinga number of layers supported by the UE.
 6. The method of claim 5,wherein a number of bits of the bitmap is determined based on the UEcapability information.
 7. The method of claim 1, wherein the bitmapcomprises a 8 bit sequence.
 8. The method of claim 1, wherein the CSI isderived based on a codebook.
 9. The method of claim 8, wherein thecodebook is a Type I single panel codebook.
 10. The method of claim 8,further comprising: receiving second information related to subsetrestriction of the codebook, wherein the second information isconfigured in a form of a bitmap, and wherein a number of bits of thebitmap of the second information is determined based on a number ofantenna ports in first domain and a number of antenna ports in seconddomain.
 11. The method of claim 10, wherein based on that (i) a totalnumber of antenna ports in the first domain and the second domain isconfigured as 16 or more and (ii) a number of layers is 3 or 4, a unitof three bits of the bitmap of the second information is associated witheach precoder, and each index of the three bits has a value associatedwith consecutive specified numbers; and wherein based on that at leastone of the three bits is configured to a value indicating the subsetrestriction of the codebook, a reporting of precoding matrix indicator(PMI) corresponding to the precoder associated with the three bits isrestricted in the CSI.
 12. The method of claim 11, wherein a bit in afirst unit of three bits belongs to a second unit of three bits.
 13. Auser equipment (UE) reporting channel state information (CSI) in awireless communication system, the UE comprising: at least onetransceiver; at least one processor; and at least one memory operablyconnected to the at least one processor and storing instructions that,based on being executed by the at least one processor, performoperations comprising: receiving, through the at least one transceiver,first information related to a restriction of a rank indicator (RI),wherein the first information is configured in a form of a bitmap, andwherein each bit of the bitmap corresponds to each of layers supportedby the UE; and transmitting, through the at least one transceiver, CSIincluding the RI, wherein a bit width of the RI is determined based onthe first information.
 14. The UE of claim 13, wherein the bit width ofthe RI is determined based on a number of bits indicating that a RIreporting associated with corresponding layer is allowed.
 15. The UE ofclaim 14, wherein values of the RI included in the CSI are mapped to thebits indicating that the RI reporting associated with correspondinglayer is allowed.
 16. A method for receiving, by a base station, channelstate information (CSI) in a wireless communication system, the methodcomprising: transmitting, to a user equipment (UE), first informationrelated to restriction of a rank indicator (RI), wherein the firstinformation is configured in a form of a bitmap, and wherein each bit ofthe bitmap corresponds to each of layers supported by the UE; andreceiving, from the UE, CSI including the RI, wherein a bit width of theRI is determined based on the first information.
 17. The method of claim16, wherein the bit width of the RI is determined based on a number ofbits indicating that a RI reporting associated with corresponding layeris allowed.
 18. The method of claim 17, wherein values of the RIincluded in the CSI are mapped to the bits indicating that the RIreporting associated with corresponding layer is allowed.